Something like this should work:
*-----
Procedure iFromyyddd
LParameter pcyyddd

return ctod("01/01/"+left(pcyyddd,2))+val(right(pcyyddd,3))-1
*---------

>Hi all.
>
>I need to convert a number in the format of 'YYDDD' (where DDD is a Julian day >number i.e. from 1 to 365 or 366 in a leap year) to a more readable date >format. Does anyone know of a function which will return a mm/dd/yy date from >this?
>
>Many thanks,
>
>Nanci