diff --git i/git-subtree.sh w/git-subtree.sh
index 781eef3..7706d72 100755
--- i/git-subtree.sh
+++ w/git-subtree.sh
@@ -27,6 +27,7 @@ onto=         try connecting new tree to an existing one
 rejoin        merge the new branch back into HEAD
  options for 'add', 'merge', 'pull' and 'push'
 squash        merge subtree changes as a single commit
+prune         prune history
 "
 eval $(echo "$OPTS_SPEC" | git rev-parse --parseopt -- "$@" || echo exit $?)
 
@@ -44,6 +45,7 @@ rejoin=
 ignore_joins=
 annotate=
 squash=
+prune=
 message=
 
 debug()
@@ -92,6 +94,8 @@ while [ $# -gt 0 ]; do
 		--no-ignore-joins) ignore_joins= ;;
 		--squash) squash=1 ;;
 		--no-squash) squash= ;;
+		--prune) prune=1;;
+		--no-prune) prune=;;
 		--) break ;;
 		*) die "Unexpected option: $opt" ;;
 	esac
@@ -110,7 +114,7 @@ if [ -z "$prefix" ]; then
 fi
 
 case "$command" in
-	add) [ -e "$prefix" ] && 
+	add) [ -e "$prefix" -a -z "$prune" ] &&
 		die "prefix '$prefix' already exists." ;;
 	*)   [ -e "$prefix" ] || 
 		die "'$prefix' does not exist; use 'git subtree add'" ;;
@@ -359,6 +363,17 @@ squash_msg()
 	echo "git-subtree-split: $newsub"
 }
 
+prune_msg()
+{
+	dir="$1"
+	newsub="$2"
+	
+	git show -s --pretty="tformat:Subtree '$dir/': %h %s" $newsub
+	echo
+	echo "git-subtree-dir: $dir"
+	echo "git-subtree-split: $newsub"
+}
+
 toptree_for_commit()
 {
 	commit="$1"
@@ -464,7 +479,7 @@ ensure_clean()
 
 cmd_add()
 {
-	if [ -e "$dir" ]; then
+	if [ -e "$dir" -a -z "$prune" ]; then
 		die "'$dir' already exists.  Cannot add."
 	fi
 
@@ -498,6 +513,10 @@ cmd_add_commit()
 	rev="$1"
 	
 	debug "Adding $dir as '$rev'..."
+	if [ -d "$dir" ]; then
+	    #TODO: write it with plumbing commands
+	    git rm -r -q $dir
+	fi
 	git read-tree --prefix="$dir" $rev || exit $?
 	git checkout -- "$dir" || exit $?
 	tree=$(git write-tree) || exit $?
@@ -513,6 +532,9 @@ cmd_add_commit()
 		rev=$(new_squash_commit "" "" "$rev") || exit $?
 		commit=$(add_squashed_msg "$rev" "$dir" |
 			 git commit-tree $tree $headp -p "$rev") || exit $?
+	elif [ -n "$prune" ]; then
+		commit=$(prune_msg "$dir" "$rev" |
+			 git commit-tree $tree -p $headrev) || exit $?
 	else
 		commit=$(add_msg "$dir" "$headrev" "$rev" |
 			 git commit-tree $tree $headp -p "$rev") || exit $?