diff --git a/hgext/show.py b/hgext/show.py
--- a/hgext/show.py
+++ b/hgext/show.py
@@ -161,9 +161,10 @@
             ui.write(_('(no bookmarks set)\n'))
         return
 
+    revs = [repo[node].rev() for node in marks.values()]
     active = repo._activebookmark
     longestname = max(len(b) for b in marks)
-    # TODO consider exposing longest shortest(node).
+    nodelen = longestshortest(repo, revs)
 
     for bm, node in sorted(marks.items()):
         fm.startitem()
@@ -172,7 +173,7 @@
         fm.write('node', fm.hexfunc(node), fm.hexfunc(node))
         fm.data(active=bm == active,
                 longestbookmarklen=longestname,
-                nodelen=5)
+                nodelen=nodelen)
 
 @showview('stack', csettopic='stack')
 def showstack(ui, repo, displayer):
@@ -236,6 +237,9 @@
     else:
         newheads = set()
 
+    allrevs = set(stackrevs) | newheads | set([baserev])
+    nodelen = longestshortest(repo, allrevs)
+
     try:
         cmdutil.findcmd('rebase', commands.table)
         haverebase = True
@@ -247,7 +251,7 @@
     # our simplicity and the customizations required.
     # TODO use proper graph symbols from graphmod
 
-    shortesttmpl = formatter.maketemplater(ui, '{shortest(node, 5)}')
+    shortesttmpl = formatter.maketemplater(ui, '{shortest(node, %d)}' % nodelen)
     def shortest(ctx):
         return shortesttmpl.render({'ctx': ctx, 'node': ctx.hex()})
 
@@ -278,7 +282,7 @@
                 ui.write('  ')
 
             ui.write(('o  '))
-            displayer.show(ctx, nodelen=5)
+            displayer.show(ctx, nodelen=nodelen)
             displayer.flush(ctx)
             ui.write('\n')
 
@@ -318,7 +322,7 @@
             ui.write('  ')
 
         ui.write(symbol, '  ')
-        displayer.show(ctx, nodelen=5)
+        displayer.show(ctx, nodelen=nodelen)
         displayer.flush(ctx)
         ui.write('\n')
 
@@ -335,7 +339,7 @@
         ui.write(_('(stack base)'), '\n', label='stack.label')
         ui.write(('o  '))
 
-        displayer.show(basectx, nodelen=5)
+        displayer.show(basectx, nodelen=nodelen)
         displayer.flush(basectx)
         ui.write('\n')
 
@@ -394,12 +398,13 @@
     """changesets that aren't finished"""
     # TODO support date-based limiting when calling revset.
     revs = repo.revs('sort(_underway(), topo)')
+    nodelen = longestshortest(repo, revs)
 
     revdag = graphmod.dagwalker(repo, revs)
 
     ui.setconfig('experimental', 'graphshorten', True)
     cmdutil.displaygraph(ui, repo, revdag, displayer, graphmod.asciiedges,
-                         props={'nodelen': 5})
+                         props={'nodelen': nodelen})
 
 def extsetup(ui):
     # Alias `hg <prefix><view>` to `hg show <view>`.
@@ -420,6 +425,27 @@
 
             ui.setconfig('alias', name, 'show %s' % view, source='show')
 
+def longestshortest(repo, revs, minlen=4):
+    """Return the length of the longest shortest node to identify revisions.
+
+    The result of this function can be used with the ``shortest()`` template
+    function to ensure that a value is unique and unambiguous for a given
+    set of nodes.
+
+    The number of revisions in the repo is taken into account to prevent
+    a numeric node prefix from conflicting with an integer revision number.
+    If we fail to do this, a value of e.g. ``10023`` could mean either
+    revision 10023 or node ``10023abc...``.
+    """
+    tmpl = formatter.maketemplater(repo.ui, '{shortest(node, %d)}' % minlen)
+    lens = [minlen]
+    for rev in revs:
+        ctx = repo[rev]
+        shortest = tmpl.render({'ctx': ctx, 'node': ctx.hex()})
+        lens.append(len(shortest))
+
+    return max(lens)
+
 # Adjust the docstring of the show command so it shows all registered views.
 # This is a bit hacky because it runs at the end of module load. When moved
 # into core or when another extension wants to provide a view, we'll need
diff --git a/tests/test-show-stack.t b/tests/test-show-stack.t
--- a/tests/test-show-stack.t
+++ b/tests/test-show-stack.t
@@ -17,7 +17,7 @@
   $ echo 0 > foo
   $ hg -q commit -A -m 'commit 0'
   $ hg show stack
-    @  9f171 commit 0
+    @  9f17 commit 0
 
 Stack displays multiple draft changesets
 
@@ -30,48 +30,48 @@
   $ echo 4 > foo
   $ hg commit -m 'commit 4'
   $ hg show stack
-    @  2737b commit 4
-    o  d1a69 commit 3
-    o  128c8 commit 2
-    o  181cc commit 1
-    o  9f171 commit 0
+    @  2737 commit 4
+    o  d1a6 commit 3
+    o  128c commit 2
+    o  181c commit 1
+    o  9f17 commit 0
 
 Public parent of draft base is displayed, separated from stack
 
   $ hg phase --public -r 0
   $ hg show stack
-    @  2737b commit 4
-    o  d1a69 commit 3
-    o  128c8 commit 2
-    o  181cc commit 1
+    @  2737 commit 4
+    o  d1a6 commit 3
+    o  128c commit 2
+    o  181c commit 1
    /   (stack base)
-  o  9f171 commit 0
+  o  9f17 commit 0
 
   $ hg phase --public -r 1
   $ hg show stack
-    @  2737b commit 4
-    o  d1a69 commit 3
-    o  128c8 commit 2
+    @  2737 commit 4
+    o  d1a6 commit 3
+    o  128c commit 2
    /   (stack base)
-  o  181cc commit 1
+  o  181c commit 1
 
 Draft descendants are shown
 
   $ hg -q up 2
   $ hg show stack
-    o  2737b commit 4
-    o  d1a69 commit 3
-    @  128c8 commit 2
+    o  2737 commit 4
+    o  d1a6 commit 3
+    @  128c commit 2
    /   (stack base)
-  o  181cc commit 1
+  o  181c commit 1
 
   $ hg -q up 3
   $ hg show stack
-    o  2737b commit 4
-    @  d1a69 commit 3
-    o  128c8 commit 2
+    o  2737 commit 4
+    @  d1a6 commit 3
+    o  128c commit 2
    /   (stack base)
-  o  181cc commit 1
+  o  181c commit 1
 
 working dir on public changeset should display special message
 
@@ -89,10 +89,10 @@
   $ hg show stack
    \ /  (multiple children)
     |
-    o  d1a69 commit 3
-    @  128c8 commit 2
+    o  d1a6 commit 3
+    @  128c commit 2
    /   (stack base)
-  o  181cc commit 1
+  o  181c commit 1
 
   $ cd ..
 
@@ -117,9 +117,9 @@
 TODO doesn't yet handle case where wdir is a draft merge
 
   $ hg show stack
-    @  8ee90 merge heads
+    @  8ee9 merge heads
    /   (stack base)
-  o  59478 head 1
+  o  5947 head 1
 
   $ echo d1 > foo
   $ hg commit -m 'draft 1'
@@ -127,10 +127,10 @@
   $ hg commit -m 'draft 2'
 
   $ hg show stack
-    @  430d5 draft 2
-    o  787b1 draft 1
+    @  430d draft 2
+    o  787b draft 1
    /   (stack base)
-  o  8ee90 merge heads
+  o  8ee9 merge heads
 
   $ cd ..
 
@@ -156,36 +156,36 @@
 Newer draft heads don't impact output
 
   $ hg show stack
-    @  eaffc draft 2
-    o  2b218 draft 1
+    @  eaff draft 2
+    o  2b21 draft 1
    /   (stack base)
-  o  b66bb base
+  o  b66b base
 
 Newer public heads are rendered
 
   $ hg phase --public -r '::tip'
 
   $ hg show stack
-    o  baa4b new 2
+    o  baa4 new 2
    /    (2 commits ahead)
   :
   :    (stack head)
-  : @  eaffc draft 2
-  : o  2b218 draft 1
+  : @  eaff draft 2
+  : o  2b21 draft 1
   :/   (stack base)
-  o  b66bb base
+  o  b66b base
 
 If rebase is available, we show a hint how to rebase to that head
 
   $ hg --config extensions.rebase= show stack
-    o  baa4b new 2
-   /    (2 commits ahead; hg rebase --source 2b218 --dest baa4b)
+    o  baa4 new 2
+   /    (2 commits ahead; hg rebase --source 2b21 --dest baa4)
   :
   :    (stack head)
-  : @  eaffc draft 2
-  : o  2b218 draft 1
+  : @  eaff draft 2
+  : o  2b21 draft 1
   :/   (stack base)
-  o  b66bb base
+  o  b66b base
 
 Similar tests but for multiple heads
 
@@ -196,25 +196,25 @@
   $ hg -q up 2
 
   $ hg show stack
-    o  baa4b new 2
+    o  baa4 new 2
    /    (2 commits ahead)
-  : o  9a848 new head 2
+  : o  9a84 new head 2
   :/    (1 commits ahead)
   :
   :    (stack head)
-  : @  eaffc draft 2
-  : o  2b218 draft 1
+  : @  eaff draft 2
+  : o  2b21 draft 1
   :/   (stack base)
-  o  b66bb base
+  o  b66b base
 
   $ hg --config extensions.rebase= show stack
-    o  baa4b new 2
-   /    (2 commits ahead; hg rebase --source 2b218 --dest baa4b)
-  : o  9a848 new head 2
-  :/    (1 commits ahead; hg rebase --source 2b218 --dest 9a848)
+    o  baa4 new 2
+   /    (2 commits ahead; hg rebase --source 2b21 --dest baa4)
+  : o  9a84 new head 2
+  :/    (1 commits ahead; hg rebase --source 2b21 --dest 9a84)
   :
   :    (stack head)
-  : @  eaffc draft 2
-  : o  2b218 draft 1
+  : @  eaff draft 2
+  : o  2b21 draft 1
   :/   (stack base)
-  o  b66bb base
+  o  b66b base
diff --git a/tests/test-show-work.t b/tests/test-show-work.t
--- a/tests/test-show-work.t
+++ b/tests/test-show-work.t
@@ -16,20 +16,20 @@
   $ hg -q commit -A -m 'commit 0'
 
   $ hg show work
-  @  9f171 commit 0
+  @  9f17 commit 0
 
 Even when it isn't the wdir
 
   $ hg -q up null
 
   $ hg show work
-  o  9f171 commit 0
+  o  9f17 commit 0
 
 Single changeset is still there when public because it is a head
 
   $ hg phase --public -r 0
   $ hg show work
-  o  9f171 commit 0
+  o  9f17 commit 0
 
 A draft child will show both it and public parent
 
@@ -38,8 +38,8 @@
   $ hg commit -m 'commit 1'
 
   $ hg show work
-  @  181cc commit 1
-  o  9f171 commit 0
+  @  181c commit 1
+  o  9f17 commit 0
 
 Multiple draft children will be shown
 
@@ -47,16 +47,16 @@
   $ hg commit -m 'commit 2'
 
   $ hg show work
-  @  128c8 commit 2
-  o  181cc commit 1
-  o  9f171 commit 0
+  @  128c commit 2
+  o  181c commit 1
+  o  9f17 commit 0
 
 Bumping first draft changeset to public will hide its parent
 
   $ hg phase --public -r 1
   $ hg show work
-  @  128c8 commit 2
-  o  181cc commit 1
+  @  128c commit 2
+  o  181c commit 1
   |
   ~
 
@@ -68,10 +68,10 @@
   created new head
 
   $ hg show work
-  @  f0abc commit 3
-  | o  128c8 commit 2
+  @  f0ab commit 3
+  | o  128c commit 2
   |/
-  o  181cc commit 1
+  o  181c commit 1
   |
   ~
 
@@ -80,10 +80,10 @@
   $ hg -q up null
 
   $ hg show work
-  o  f0abc commit 3
-  | o  128c8 commit 2
+  o  f0ab commit 3
+  | o  128c commit 2
   |/
-  o  181cc commit 1
+  o  181c commit 1
   |
   ~
 
@@ -95,13 +95,13 @@
   created new head
 
   $ hg show work
-  @  668ca commit 4
-  | o  f0abc commit 3
-  | | o  128c8 commit 2
+  @  668c commit 4
+  | o  f0ab commit 3
+  | | o  128c commit 2
   | |/
-  | o  181cc commit 1
+  | o  181c commit 1
   |/
-  o  9f171 commit 0
+  o  9f17 commit 0
 
   $ cd ..
 
@@ -126,11 +126,11 @@
   $ hg commit -m 'commit 4'
 
   $ hg show work
-  @  f8dd3 (mybranch) commit 4
-  o  90cfc (mybranch) commit 3
-  | o  128c8 commit 2
+  @  f8dd (mybranch) commit 4
+  o  90cf (mybranch) commit 3
+  | o  128c commit 2
   |/
-  o  181cc commit 1
+  o  181c commit 1
   |
   ~
 
@@ -157,11 +157,11 @@
   $ hg bookmark mybook
 
   $ hg show work
-  @  cac82 (mybook) commit 4
-  o  f0abc commit 3
-  | o  128c8 (@) commit 2
+  @  cac8 (mybook) commit 4
+  o  f0ab commit 3
+  | o  128c (@) commit 2
   |/
-  o  181cc commit 1
+  o  181c commit 1
   |
   ~
 
@@ -182,9 +182,9 @@
   $ hg tag 0.2
 
   $ hg show work
-  @  37582 Added tag 0.2 for changeset 6379c25b76f1
-  o  6379c (0.2) commit 3
-  o  a2ad9 Added tag 0.1 for changeset 6a75536ea0b1
+  @  3758 Added tag 0.2 for changeset 6379c25b76f1
+  o  6379 (0.2) commit 3
+  o  a2ad Added tag 0.1 for changeset 6a75536ea0b1
   |
   ~
 
@@ -205,15 +205,15 @@
   $ hg commit -m 'commit 2'
 
   $ hg show work
-  @  34834 (mybook) (mybranch) commit 2
-  o  97fcc commit 1
+  @  3483 (mybook) (mybranch) commit 2
+  o  97fc commit 1
 
 Multiple bookmarks on same changeset render properly
 
   $ hg book mybook2
   $ hg show work
-  @  34834 (mybook mybook2) (mybranch) commit 2
-  o  97fcc commit 1
+  @  3483 (mybook mybook2) (mybranch) commit 2
+  o  97fc commit 1
 
   $ cd ..
 
@@ -230,8 +230,38 @@
   $ hg commit -m 'commit 3'
 
   $ hg --config extensions.revnames=$TESTDIR/revnamesext.py show work
-  @  32f3e (r2) commit 3
-  o  6a755 (r1) commit 2
-  o  97fcc (r0) commit 1
+  @  32f3 (r2) commit 3
+  o  6a75 (r1) commit 2
+  o  97fc (r0) commit 1
 
   $ cd ..
+
+Prefix collision on hashes increases shortest node length
+
+  $ hg init hashcollision
+  $ cd hashcollision
+  $ echo 0 > a
+  $ hg -q commit -Am 0
+  $ for i in 17 1057 2857 4025; do
+  >   hg -q up 0
+  >   echo $i > a
+  >   hg -q commit -m $i
+  >   echo 0 > a
+  >   hg commit -m "$i commit 2"
+  > done
+
+  $ hg show work
+  @  cfd04 4025 commit 2
+  o  c562d 4025
+  | o  08048 2857 commit 2
+  | o  c5623 2857
+  |/
+  | o  6a6b6 1057 commit 2
+  | o  c5625 1057
+  |/
+  | o  96b4e 17 commit 2
+  | o  11424 17
+  |/
+  o  b4e73 0
+
+  $ cd ..
diff --git a/tests/test-show.t b/tests/test-show.t
--- a/tests/test-show.t
+++ b/tests/test-show.t
@@ -95,8 +95,8 @@
   $ hg bookmark a-longer-bookmark
 
   $ hg show bookmarks
-  * a-longer-bookmark    7b570
-    book1                b757f
+  * a-longer-bookmark    7b57
+    book1                b757
 
 A custom bookmarks template works
 
@@ -113,14 +113,14 @@
     "bookmark": "a-longer-bookmark",
     "longestbookmarklen": 17,
     "node": "7b5709ab64cbc34da9b4367b64afff47f2c4ee83",
-    "nodelen": 5
+    "nodelen": 4
    },
    {
     "active": false,
     "bookmark": "book1",
     "longestbookmarklen": 17,
     "node": "b757f780b8ffd71267c6ccb32e0882d9d32a8cc0",
-    "nodelen": 5
+    "nodelen": 4
    }
   ]
 
@@ -138,19 +138,19 @@
   (no bookmarks set)
 
   $ hg --config commands.show.aliasprefix=sh shwork
-  @  7b570 commit for book2
-  o  b757f commit for book1
-  o  ba592 initial
+  @  7b57 commit for book2
+  o  b757 commit for book1
+  o  ba59 initial
 
   $ hg --config commands.show.aliasprefix='s sh' swork
-  @  7b570 commit for book2
-  o  b757f commit for book1
-  o  ba592 initial
+  @  7b57 commit for book2
+  o  b757 commit for book1
+  o  ba59 initial
 
   $ hg --config commands.show.aliasprefix='s sh' shwork
-  @  7b570 commit for book2
-  o  b757f commit for book1
-  o  ba592 initial
+  @  7b57 commit for book2
+  o  b757 commit for book1
+  o  ba59 initial
 
 The aliases don't appear in `hg config`