Audrina Patridge celebrated her birthday (her actual birthday was May 9) in Las Vegas Saturday night - without Hills BFF Lauren Conrad.

But The Hills star still had fun, not to worry.

Drinking Grey Goose and Red Bull and goofing off with pals â€" including her mom! â€" Audrina Patridge had a blast, and netted a fat paycheck at club LAX.

Check out the photo below ...

The Hills' Audrina Patridge is 23... and pretty.