diff -ru mutt-1.5.6.orig/init.h mutt-1.5.6/init.h
--- mutt-1.5.6.orig/init.h	2004-02-01 18:15:17.000000000 +0100
+++ mutt-1.5.6/init.h	2004-06-21 22:58:49.000000000 +0200
@@ -704,6 +704,13 @@
   ** When set, mutt will not show the presence of missing messages in the
   ** thread tree.
   */
+  { "hide_thread_subject", DT_BOOL, R_TREE|R_INDEX, OPTHIDETHREADSUBJECT, 1 },
+  /*
+  ** .pp
+  ** When set, mutt will not show the subject of messages in the thread
+  ** tree that have the same subject as their parent or closest previously
+  ** displayed sibling.
+  */
   { "hide_top_limited",	DT_BOOL, R_TREE|R_INDEX, OPTHIDETOPLIMITED, 0 },
   /*
   ** .pp
diff -ru mutt-1.5.6.orig/mutt.h mutt-1.5.6/mutt.h
--- mutt-1.5.6.orig/mutt.h	2004-02-01 18:15:17.000000000 +0100
+++ mutt-1.5.6/mutt.h	2004-06-21 22:48:35.000000000 +0200
@@ -351,6 +351,7 @@
   OPTHIDDENHOST,
   OPTHIDELIMITED,
   OPTHIDEMISSING,
+  OPTHIDETHREADSUBJECT,
   OPTHIDETOPLIMITED,
   OPTHIDETOPMISSING,
   OPTIGNORELISTREPLYTO,
diff -ru mutt-1.5.6.orig/PATCHES mutt-1.5.6/PATCHES
--- mutt-1.5.6.orig/PATCHES	2004-02-01 18:42:47.000000000 +0100
+++ mutt-1.5.6/PATCHES	2004-06-21 21:54:50.000000000 +0200
@@ -0,0 +1 @@
+patch-1.5.6.eh.thread_subject.1
diff -ru mutt-1.5.6.orig/thread.c mutt-1.5.6/thread.c
--- mutt-1.5.6.orig/thread.c	2004-02-01 18:10:58.000000000 +0100
+++ mutt-1.5.6/thread.c	2004-06-21 22:51:35.000000000 +0200
@@ -41,6 +41,10 @@
 {
   THREAD *tmp, *tree = hdr->thread;
 
+  /* if the user disabled subject hiding, display it */
+  if (!option (OPTHIDETHREADSUBJECT))
+    return (1);
+
   /* if our subject is different from our parent's, display it */
   if (hdr->subject_changed)
     return (1);