Index: src/parser/ArcanistDiffParser.php
===================================================================
--- src/parser/ArcanistDiffParser.php
+++ src/parser/ArcanistDiffParser.php
@@ -205,6 +205,8 @@
         // This is a git diff, probably from "git show" or "git diff".
         // Note that the filenames may appear quoted.
         '(?P<type>diff --git) (?P<oldnew>.*)',
+        // RCS Diff
+        '(?P<type>rcsdiff -u) (?P<oldnew>.*)',
         // This is a unified diff, probably from "diff -u" or synthetic diffing.
         '(?P<type>---) (?P<old>.+)\s+\d{4}-\d{2}-\d{2}.*',
         '(?P<binary>Binary) files '.
Index: src/parser/__tests__/ArcanistDiffParserTestCase.php
===================================================================
--- src/parser/__tests__/ArcanistDiffParserTestCase.php
+++ src/parser/__tests__/ArcanistDiffParserTestCase.php
@@ -549,6 +549,20 @@
       case 'svn-property-windows.svndiff':
         $this->assertEqual(1, count($changes));
         break;
+      case 'rcs-addline.rcsdiff':
+        $this->assertEqual(1, count($changes));
+        $change = array_shift($changes);
+        $this->assertEqual(
+          ArcanistDiffChangeType::TYPE_CHANGE,
+          $change->getType());
+        break;
+      case 'rcs-deleteline.rcs.diff':
+        $this->assertEqual(1, count($changes));
+        $change = array_shift($changes);
+        $this->assertEqual(
+          ArcanistDiffChangeType::TYPE_CHANGE,
+          $change->getType());
+        break;
       default:
         throw new Exception("No test block for diff file {$diff_file}.");
         break;
Index: src/parser/__tests__/diff/rcs-addline.rcsdiff
===================================================================
--- /dev/null
+++ src/parser/__tests__/diff/rcs-addline.rcsdiff
@@ -0,0 +1,13 @@
+rcsdiff -u ./testing.php
+===================================================================
+RCS file: ./RCS/testing.php,v
+retrieving revision 1.1
+diff -u -r1.1 ./testing.php
+--- ./testing.php      2013/03/11 16:41:39    1.1
++++ ./testing.php      2013/03/11 16:44:10
+@@ -1,3 +1,4 @@
+ <?php
+ echo "Hello World";
++echo "How are you doing today?";
+ ?>
+
Index: src/parser/__tests__/diff/rcs-deleteline.rcsdiff
===================================================================
--- /dev/null
+++ src/parser/__tests__/diff/rcs-deleteline.rcsdiff
@@ -0,0 +1,13 @@
+rcsdiff -u ./testing.php
+===================================================================
+RCS file: ./RCS/testing.php,v
+retrieving revision 1.2
+diff -u -r1.2 ./testing.php
+--- ./testing.php      2013/03/11 16:45:50    1.2
++++ ./testing.php      2013/03/11 16:46:19
+@@ -1,4 +1,3 @@
+ <?php
+-echo "Hello World";
+ echo "How are you doing today?";
+ ?>
+