Right, if that's the case, an empty date in dob would generate an error and NULL will be treated as current date.
See Birthday Query in VFP for a query that handles empty and null dates w/o additional checks.

>to be picky, if dob can be empty or null then

>where !empty(dob) and !isnull(dob) and 
>		(	DATE( YEAR( ldStart ), MONTH( dob ), DAY( dob ) ) BETWEEN ldStart AND ldEnd
>		OR 
>			DATE( YEAR( ldEnd), MONTH( dob ), DAY( dob ) ) BETWEEN ldStart AND ldEnd)
>