Elvira: Good Genes or Good Docs?

Elvira, Mistress of the Dark aka Cassandra Peterson is anything but a horror.

Here's the 39-year-old goth babe back in 1990 (left) -- and 22 years later, the buxom 61-year-old at an event in L.A. last month (right).

The scariest thing about Elvira ... she doesn't age.