>In my application, users are allowed to modify the structure of some files. A loop checks if essential fields have been tampered with and forces the fields back in place. But if they screw up and decide to Cancel the FoxPro Modi Struc form, can I trap that after the modi struc command in my code? Thanks in advance...

Not something I would allow but...

If you are using MODI STRU directly, then when they cancel, the structure will remain unchanged.

I would recommend making a backup of your structure and data if possible, just before the modi stru. After they are done compare the fields with AFIELDS() and take appropriate action (of course check all properties not just the names)