diff --git a/TODO b/TODO
index 399e3a1f..7a323edf 100644
--- a/TODO
+++ b/TODO
@@ -15,7 +15,7 @@ v "string"
 assq
 call-with-values
 v char?
-length
+v length
 v list
 list->vector
 make-vector
diff --git a/mes.c b/mes.c
index d02b0ba6..7a255080 100644
--- a/mes.c
+++ b/mes.c
@@ -560,6 +560,18 @@ string_length (scm *x)
   return make_number (strlen (x->name));
 }
 
+scm *
+length (scm *x)
+{
+  int n = 0;
+  while (x != &scm_nil)
+    {
+      n++;
+      x = cdr (x);
+    }
+  return make_number (n);
+}
+
 scm *
 lookup (char *x, scm *a)
 {
diff --git a/test.mes b/test.mes
index 2eff4e96..f1215dc8 100644
--- a/test.mes
+++ b/test.mes
@@ -182,4 +182,11 @@
 (display (string #\a #\space #\s #\t #\r #\i #\n #\g #\newline))
 (newline)
 
+(display "length of nil: ")
+(display (length '()))
+(newline)
+(display "length of '(a b c): ")
+(display (length '(a b c)))
+(newline)
+
 '()