diff --git a/collects/redex/private/matcher.ss b/collects/redex/private/matcher.ss
index 6e9a2beff3..c3f00cca55 100644
--- a/collects/redex/private/matcher.ss
+++ b/collects/redex/private/matcher.ss
@@ -1592,6 +1592,7 @@ before the pattern compiler is invoked.
                       compiled-pattern?))
  
  (set-cache-size! (-> (and/c integer? positive?) void?))
+ (cache-size (and/c integer? positive?))
  
  (make-bindings ((listof bind?) . -> . bindings?))
  (bindings-table (bindings? . -> . (listof bind?)))
diff --git a/collects/redex/private/reduction-semantics.ss b/collects/redex/private/reduction-semantics.ss
index c082c6546d..4fdca8fbfd 100644
--- a/collects/redex/private/reduction-semantics.ss
+++ b/collects/redex/private/reduction-semantics.ss
@@ -1425,7 +1425,15 @@
     (values
      (wrap
       (letrec ([cache (make-hash)]
+               [cache-entries 0]
                [not-in-cache (gensym)]
+               [cache-result (λ (arg res case)
+                               (when (caching-enabled?)
+                                 (when (>= cache-entries cache-size)
+                                   (set! cache (make-hash))
+                                   (set! cache-entries 0))
+                                 (hash-set! cache arg (cons res case))
+                                 (set! cache-entries (add1 cache-entries))))]
                [log-coverage (λ (id)
                                (when id
                                  (for-each 
@@ -1452,7 +1460,7 @@
                            [(null? cases) 
                             (if relation?
                                 (begin 
-                                  (hash-set! cache exp (cons #f #f))
+                                  (cache-result exp #f #f)
                                   #f)
                                 (redex-error name "no clauses matched for ~s" `(,name . ,exp)))]
                            [else
@@ -1470,7 +1478,7 @@
                                        (redex-error name "codomain test failed for ~s, call was ~s" ans `(,name ,@exp)))
                                      (cond
                                        [ans 
-                                        (hash-set! cache exp (cons #t id))
+                                        (cache-result exp #t id)
                                         (log-coverage id)
                                         #t]
                                        [else
@@ -1499,7 +1507,7 @@
                                                          "codomain test failed for ~s, call was ~s"
                                                          ans 
                                                          `(,name ,@exp)))
-                                          (hash-set! cache exp (cons ans id))
+                                          (cache-result exp ans id)
                                           (log-coverage id)
                                           ans)]))])))]))]
                       [else 
diff --git a/collects/redex/redex.scrbl b/collects/redex/redex.scrbl
index f53615be1c..7d99f20667 100644
--- a/collects/redex/redex.scrbl
+++ b/collects/redex/redex.scrbl
@@ -369,28 +369,19 @@ clause is followed by an ellipsis.  Nested ellipses produce
 nested lists.
 }
 
-@defproc[(set-cache-size! [size positive-integer?]) void?]{
-
-Changes the cache size; the default size is @scheme[350].
-
-The cache is per-pattern (ie, each pattern has a cache of size at most
-350 (by default)) and is a simple table that maps expressions to how
-they matched the pattern (ie, the bindings for the pattern
-variables). When the cache gets full, it is thrown away and a new
-cache is started.
+@defparam[caching-enabled? on? boolean?]{
+  When this parameter is @scheme[#t] (the default), Redex caches the results of 
+  pattern matching and metafunction evaluation. There is a separate cache for
+  each pattern and metafunction; when one fills (see @scheme[set-cache-size!]),
+  Redex evicts all of the entries in that cache.
+                                         
+  Caching should be disabled when matching a pattern that depends on values
+  other than the in-scope pattern variables or evaluating a metafunction
+  that reads or writes mutable external state.
 }
 
-@defparam[caching-enabled? on? boolean?]{
-  This is a parameter that controls whether or not a cache
-  is consulted (and updated) while matching and while evaluating
-  metafunctions.
-
-  If it is @scheme[#t], then side-conditions and the right-hand sides
-  of metafunctions are assumed to only depend on the values of the
-  pattern variables in scope (and thus not on any other external
-  state).
-
-  Defaults to @scheme[#t].
+@defproc[(set-cache-size! [size positive-integer?]) void?]{                                                           
+Changes the size of the per-pattern and per-metafunction caches. The default size is @scheme[350].
 }
 
 @section{Terms}
@@ -921,7 +912,7 @@ or if the contract is violated.
 
 Note that metafunctions are assumed to always return the same results
 for the same inputs, and their results are cached, unless
-@scheme[caching-enable?] is set to @scheme[#f]. Accordingly, if a
+@scheme[caching-enabled?] is set to @scheme[#f]. Accordingly, if a
 metafunction is called with the same inputs twice, then its body is
 only evaluated a single time.