Hi Andy,
My bad, I actually meant ("MouseMove" - typo).
It sounds like you're working directly in a worksheet, rather than a UserForm?
If your 'listbox' is actually a Data Validation list, then you could check out http://www.contextures.com/excel-data-validation-multiple.html for some tips.
If you're using the ActiveX control ListBox in the worksheet, then you should be able to make use of the MouseOver event. In Design Mode, right-click the listbox and select "View Code" - this should open up the VBA window. You should see two dropdown boxes at the top of the Code window, the left one should show the name of your listbox (e.g., "ListBox1") and the right one should contain a list of events. Select the MouseMove event from the right box - this will automatically add a sub to the code window that will run whenever the mouse is moved over the listbox. Just type whatever code you want in this sub, e.g.,
.
I was working in a UserForm, so I could use a similair approach but on the UserForm object itself to make the listbox small again when the mouse wasn't over the listbox - but perhaps you could use the "LostFocus" event to resize the listbox.
Hope this helps.
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