вот что пишет на эту тему Peter Below [TeamB]:

Since the scrollbars do not belong to the MDI frame
window itself, they belong to the client window, which is not a Delphi
form. Which means one has to attack the problem on the API level.
Since this question has come up so frequently in recent days i have
modified a sample based on the stock MDI project to include this
feature. The salient parts are quoted below.

Open the main forms unit in the IDE.
If you don't have a handler for the OnCreate event, add one. In the
handler you do this:



Add a new standalone function to the unit, it has to go above the
FormCreate method since it is referenced in the statement above.



I clipped this code from a larger project, so lets hope i did not
create errors in the process. What this code does is to subclass the
client window the API way. It stores the old window function into the
GWL_USERDATA field of the window structure since it is needed in the
replacement window function, all messages need to be passed on to the
old window function. There is only one message of interest in this case
(the use of a Case results from the larger project, which handles more
than this message): WM_NCCALCSIZE. The window gets this message when
Windows tries to hide or show the scrollbars, among other cases. And it
arrives *before* there is any painting of the scrollbar. So we can
check if the window is going to sprout scrollbars and simply remove the
scrollbar styles again.

For the purists: there is no need to undo the subclassing before the
form is destroyed since the client window is destroyed before the form
object.

Peter Below (TeamB)