Judy Greer -- Good Genes or Good Docs?

Judy Greer's looks are screamin' good!

Here's a 25-year-old version of the '13 Going On 30' actress at a movie premiere in California back in 2001 (left) and 17-years-later ... The 'Halloween' star was seen looking better than ever while at an event in Hollywood last week (right).

No tricks ... just treats!

The question is ...