Do a Google search on "validate social security numbers" and you'll find lots of references that may help. Validating the pattern is easy, of course; just check for three digits followed by a dash followed by two digits followed by another dash followed by four digits, as in 999-99-9999. I don't know if there is an algorithm to validate the entire number, but I believe the first 3 digits have something to do with the person's address (geographic location in the U.S.) at the time their number was issued. There may be other information embedded in the number as well.

>Dear all
>
>I am translating my software to English and also making some
>structural changes to it in order to reach american users
>
>In Brazil our national indenfication document is CPF.
>CPF is a 11 digits string that has a logic and is possible to validate by a function.
>
>I would like to know if SSN is also a logic string, and a function in VFP is available to validade it
>
>Regards
>
>Moises