diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -2843,6 +2843,7 @@ def debugrevlog(ui, repo, file_=None, **
         deltasize[2] /= numrevs - numfull
     totalsize = fulltotal + deltatotal
     avgchainlen = sum(chainlengths) / numrevs
+    maxchainlen = max(chainlengths)
     compratio = totalrawsize / totalsize
 
     basedfmtstr = '%%%dd\n'
@@ -2875,6 +2876,7 @@ def debugrevlog(ui, repo, file_=None, **
     ui.write('\n')
     fmt = dfmtstr(max(avgchainlen, compratio))
     ui.write(('avg chain length  : ') + fmt % avgchainlen)
+    ui.write(('max chain length  : ') + fmt % maxchainlen)
     ui.write(('compression ratio : ') + fmt % compratio)
 
     if format > 0:
diff --git a/tests/test-debugcommands.t b/tests/test-debugcommands.t
--- a/tests/test-debugcommands.t
+++ b/tests/test-debugcommands.t
@@ -18,6 +18,7 @@
       deltas    :  0 ( 0.00%)
   
   avg chain length  : 0
+  max chain length  : 0
   compression ratio : 0
   
   uncompressed data size (min/max/avg) : 43 / 43 / 43