Do you have some code where we could look at ?
It would be easier to understand what your problem is.
How do you use Forms with the Tab Control ?
Couldn't you use Panels instead, and use Visble=True and Visble=False to show and hide the Panels ?
As derez said, only the main or first Form closes the application when clickig on the close button. On Subforms, clicking on the close button only hides this Subform.
Each Form has it's own Close event.
Best regards.