diff --git a/collects/drscheme/private/main.ss b/collects/drscheme/private/main.ss
index 40e6d5eb1c..050142673e 100644
--- a/collects/drscheme/private/main.ss
+++ b/collects/drscheme/private/main.ss
@@ -57,6 +57,7 @@
                                      (finder:default-filters)))
       (application:current-app-name (string-constant drscheme))
 
+  (preferences:set-default 'drscheme:unit-window-max? #f boolean?)
   (preferences:set-default 'drscheme:frame:initial-position #f 
                            (λ (x) (or (not x)
                                       (and (pair? x)
diff --git a/collects/drscheme/private/unit.ss b/collects/drscheme/private/unit.ss
index 0444d80419..62a7c7c09d 100644
--- a/collects/drscheme/private/unit.ss
+++ b/collects/drscheme/private/unit.ss
@@ -1157,9 +1157,6 @@ module browser threading seems wrong.
                    file-menu:get-revert-item
                    file-menu:get-print-item)
           
-          (define/override (on-move x y)
-            (preferences:set 'drscheme:frame:initial-position (cons x y)))
-
           ;; logging : (union #f string[directory-name])
           (field [logging #f]
                  [definitions-log-counter 0]  ;; number
@@ -2043,11 +2040,15 @@ module browser threading seems wrong.
           
           (inherit get-menu-bar get-focus-object get-edit-target-object)
           
-          (define/override on-size
-            (lambda (w h)
-              (preferences:set 'drscheme:unit-window-width w)
-              (preferences:set 'drscheme:unit-window-height h)
-              (super on-size w h)))
+          (inherit is-maximized?)
+          (define/override (on-size w h)
+            (preferences:set 'drscheme:unit-window-width w)
+            (preferences:set 'drscheme:unit-window-height h)
+            (preferences:set 'drscheme:unit-window-max? (is-maximized?))
+            (super on-size w h))
+          
+          (define/override (on-move x y)
+            (preferences:set 'drscheme:frame:initial-position (cons x y)))
           
           (define/override (get-editor) definitions-text)
           (define/override (get-canvas)
@@ -3611,14 +3612,17 @@ module browser threading seems wrong.
              (create-new-drscheme-frame name)])]))
     
     (define first-frame? #t)
-      (define (create-new-drscheme-frame filename)
-        (let* ([drs-frame% (drscheme:get/extend:get-unit-frame)]
-               [frame (new drs-frame% (filename filename))])
-          (send (send frame get-interactions-text) initialize-console)
-          (when first-frame?
-            (let ([pos (preferences:get 'drscheme:frame:initial-position)])
-              (when pos
-                (send frame move (car pos) (cdr pos)))))
-          (set! first-frame? #f)
-          (send frame show #t)
-          frame))))
+    (define (create-new-drscheme-frame filename)
+      (let* ([drs-frame% (drscheme:get/extend:get-unit-frame)]
+             [frame (new drs-frame% (filename filename))])
+        (send (send frame get-interactions-text) initialize-console)
+        (when first-frame?
+          (let ([pos (preferences:get 'drscheme:frame:initial-position)])
+            (when pos
+              (send frame move (car pos) (cdr pos))))
+          (unless (eq? (system-type) 'macosx)
+            ;; mac os x has a bug where maximizing can make the window too big.
+            (send frame maximize (preferences:get 'drscheme:unit-window-max?))))
+        (send frame show #t)
+        (set! first-frame? #f)
+        frame))))