Birthday party at the Playboy mansion!

Playboy founder Hugh Hefner is celebrating a major milestone on Monday -- his 86th birthday -- and knew just how he wanted to commemorate his big day.

On Saturday, the Mansion hosted its annual Casablanca Night party, with Hef as the guest of honor.

"Casablanca Night is a very special night at the Playboy Mansion -- screening my favorite film on my birthday weekend," Hefner tells Us Weekly of the celebration, which is open to Hef's pals and Playboy centerfolds. "We dress for the occasion and after the film, my closest friends, my girls and I share champagne and caviar by candlelight in the dining room, that is converted into Rick's Cafe."

Hefner was also feted with a special birthday cake featuring his face superimposed on Humphrey Bogart's body on the 1942 classic's original movie poster.

"Casablanca Night is a tradition that began 20 years ago and it just keeps getting better as time goes by," Hefner tells Us.