diff --git a/doc/hgrc.5.txt b/doc/hgrc.5.txt
--- a/doc/hgrc.5.txt
+++ b/doc/hgrc.5.txt
@@ -547,6 +547,12 @@ ui::
     (hashes for the repository base and for tip) in archives created by
     the hg archive command or downloaded via hgweb.
     Default is true.
+  askusername;;
+    Whether to prompt for a username when committing. If True, and
+    neither $HGUSER nor $EMAIL has been specified, then the user will
+    be prompted to enter a username.  If no username is entered, the
+    default USER@HOST is used instead.
+    Default is False.
   debug;;
     Print debugging information. True or False. Default is False.
   editor;;
diff --git a/mercurial/ui.py b/mercurial/ui.py
--- a/mercurial/ui.py
+++ b/mercurial/ui.py
@@ -331,14 +331,16 @@ class ui(object):
 
         Searched in this order: $HGUSER, [ui] section of hgrcs, $EMAIL
         and stop searching if one of these is set.
-        If not found, use ($LOGNAME or $USER or $LNAME or
-        $USERNAME) +"@full.hostname".
+        If not found and ui.askusername is True, ask the user, else use
+        ($LOGNAME or $USER or $LNAME or $USERNAME) + "@full.hostname".
         """
         user = os.environ.get("HGUSER")
         if user is None:
             user = self.config("ui", "username")
         if user is None:
             user = os.environ.get("EMAIL")
+        if user is None and self.configbool("ui", "askusername"):
+            user = self.prompt(_("Enter a commit username:"), default=None)
         if user is None:
             try:
                 user = '%s@%s' % (util.getuser(), socket.getfqdn())