Billy,

Set the form's "CloseButton" property to "No".  This deactivates the "x" and
makes them use your button to close the form.

Note that if they are allowed to close the form using Access controls in the
menu bar or by right-clicking, your "Close Button" logic will still not be
processed.

Bruce

BillyRogers,

Option one is to use data validation rules in your table (strongest) or
in your form.  Another option, especially if the validation is
complicated and depends on the values of multiple fields is to work with
the Form's Unload event. If your validation fails, set the Cancel
parameter to True and the form won't close.  This event fires whether
you close via the Close button, DoCmd.Close, closing Access, etc.

air code sample

Private Sub Form_Unload(Cancel as Integer)

'validate form before closing is allowed

If Len(txtNonBlank & "") = 0 then
  Cancel = True
  MsgBox "You must enter a value for the field NonBlank.", vbOKOnly
  txtNonBlank.SetFocus
  Exit Sub
End if

If Len(txtNeedsText & "") = 0 then
  Cancel = True
  MsgBox "You must enter a value for the field NeedsText.", vbOKOnly
  txtNeedsText.SetFocus
  Exit Sub
End if

If txtMinimum >= txtMaximum then
  Cancel = True
  MsgBox "Minimum must be less than Maxiumum", vbOKOnly
  txtMinimum.SetFocus
  Exit Sub
End Sub
---------

HTH,

Kevin