diff --git a/mercurial/filemerge.py b/mercurial/filemerge.py
--- a/mercurial/filemerge.py
+++ b/mercurial/filemerge.py
@@ -279,6 +279,7 @@
     keep as the merged version."""
     ui = repo.ui
     fd = fcd.path()
+    uipathfn = scmutil.getuipathfn(repo)
 
     # Avoid prompting during an in-memory merge since it doesn't support merge
     # conflicts.
@@ -287,7 +288,7 @@
                                                 'support file conflicts')
 
     prompts = partextras(labels)
-    prompts['fd'] = fd
+    prompts['fd'] = uipathfn(fd)
     try:
         if fco.isabsent():
             index = ui.promptchoice(
@@ -394,13 +395,14 @@
 
 def _mergecheck(repo, mynode, orig, fcd, fco, fca, toolconf):
     tool, toolpath, binary, symlink, scriptfn = toolconf
+    uipathfn = scmutil.getuipathfn(repo)
     if symlink:
         repo.ui.warn(_('warning: internal %s cannot merge symlinks '
-                       'for %s\n') % (tool, fcd.path()))
+                       'for %s\n') % (tool, uipathfn(fcd.path())))
         return False
     if fcd.isabsent() or fco.isabsent():
         repo.ui.warn(_('warning: internal %s cannot merge change/delete '
-                       'conflict for %s\n') % (tool, fcd.path()))
+                       'conflict for %s\n') % (tool, uipathfn(fcd.path())))
         return False
     return True
 
@@ -580,9 +582,10 @@
 
 def _xmerge(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels=None):
     tool, toolpath, binary, symlink, scriptfn = toolconf
+    uipathfn = scmutil.getuipathfn(repo)
     if fcd.isabsent() or fco.isabsent():
         repo.ui.warn(_('warning: %s cannot merge change/delete conflict '
-                       'for %s\n') % (tool, fcd.path()))
+                       'for %s\n') % (tool, uipathfn(fcd.path())))
         return False, 1, None
     unused, unused, unused, back = files
     localpath = _workingpath(repo, fcd)
@@ -622,7 +625,7 @@
             lambda s: procutil.shellquote(util.localpath(s)))
         if _toolbool(ui, tool, "gui"):
             repo.ui.status(_('running merge tool %s for file %s\n') %
-                           (tool, fcd.path()))
+                           (tool, uipathfn(fcd.path())))
         if scriptfn is None:
             cmd = toolpath + ' ' + args
             repo.ui.debug('launching merge tool: %s\n' % cmd)
@@ -841,6 +844,8 @@
 
     ui = repo.ui
     fd = fcd.path()
+    uipathfn = scmutil.getuipathfn(repo)
+    fduipath = uipathfn(fd)
     binary = fcd.isbinary() or fco.isbinary() or fca.isbinary()
     symlink = 'l' in fcd.flags() + fco.flags()
     changedelete = fcd.isabsent() or fco.isabsent()
@@ -864,8 +869,8 @@
             raise error.Abort(_("invalid 'python:' syntax: %s") % toolpath)
         toolpath = script
     ui.debug("picked tool '%s' for %s (binary %s symlink %s changedelete %s)\n"
-             % (tool, fd, pycompat.bytestr(binary), pycompat.bytestr(symlink),
-                    pycompat.bytestr(changedelete)))
+             % (tool, fduipath, pycompat.bytestr(binary),
+                pycompat.bytestr(symlink), pycompat.bytestr(changedelete)))
 
     if tool in internals:
         func = internals[tool]
@@ -891,9 +896,10 @@
 
     if premerge:
         if orig != fco.path():
-            ui.status(_("merging %s and %s to %s\n") % (orig, fco.path(), fd))
+            ui.status(_("merging %s and %s to %s\n") %
+                      (uipathfn(orig), uipathfn(fco.path()), fduipath))
         else:
-            ui.status(_("merging %s\n") % fd)
+            ui.status(_("merging %s\n") % fduipath)
 
     ui.debug("my %s other %s ancestor %s\n" % (fcd, fco, fca))
 
@@ -904,7 +910,7 @@
                 raise error.InMemoryMergeConflictsError('in-memory merge does '
                                                         'not support merge '
                                                         'conflicts')
-            ui.warn(onfailure % fd)
+            ui.warn(onfailure % fduipath)
         return True, 1, False
 
     back = _makebackup(repo, ui, wctx, fcd, premerge)
@@ -957,7 +963,7 @@
                     raise error.InMemoryMergeConflictsError('in-memory merge '
                                                             'does not support '
                                                             'merge conflicts')
-                ui.warn(onfailure % fd)
+                ui.warn(onfailure % fduipath)
             _onfilemergefailure(ui)
 
         return True, r, deleted
@@ -985,6 +991,7 @@
 
 def _check(repo, r, ui, tool, fcd, files):
     fd = fcd.path()
+    uipathfn = scmutil.getuipathfn(repo)
     unused, unused, unused, back = files
 
     if not r and (_toolbool(ui, tool, "checkconflicts") or
@@ -996,7 +1003,7 @@
     if 'prompt' in _toollist(ui, tool, "check"):
         checked = True
         if ui.promptchoice(_("was merge of '%s' successful (yn)?"
-                             "$$ &Yes $$ &No") % fd, 1):
+                             "$$ &Yes $$ &No") % uipathfn(fd), 1):
             r = 1
 
     if not r and not checked and (_toolbool(ui, tool, "checkchanged") or
@@ -1005,7 +1012,7 @@
         if back is not None and not fcd.cmp(back):
             if ui.promptchoice(_(" output file %s appears unchanged\n"
                                  "was merge successful (yn)?"
-                                 "$$ &Yes $$ &No") % fd, 1):
+                                 "$$ &Yes $$ &No") % uipathfn(fd), 1):
                 r = 1
 
     if back is not None and _toolbool(ui, tool, "fixeol"):
diff --git a/tests/test-merge10.t b/tests/test-merge10.t
--- a/tests/test-merge10.t
+++ b/tests/test-merge10.t
@@ -37,8 +37,9 @@
   (run 'hg heads' to see heads, 'hg merge' to merge)
   $ hg up -C 2
   0 files updated, 0 files merged, 0 files removed, 0 files unresolved
-  $ hg merge
-  merging testdir/subdir/a and testdir/a to testdir/subdir/a
+Abuse this test for also testing that merge respects ui.relative-paths
+  $ hg --cwd testdir merge --config ui.relative-paths=yes
+  merging subdir/a and a to subdir/a
   0 files updated, 1 files merged, 0 files removed, 0 files unresolved
   (branch merge, don't forget to commit)
   $ hg stat