Leonardo DiCaprio Throws Star-Studded 50th Birthday Bash

Leonardo DiCaprio turns 50 on Monday ... but he got the party started early last evening, throwing a huge, celeb-studded bash in Los Angeles.

TMZ obtained photos of the long line of stars exiting the Saturday night soiree held at a private home in the Hollywood Hills.

Check out this eye-popping list ... Tobey Maguire, Emile Hirsch, Edward Norton, Benicio Del Toro, Jamie Foxx, Bill Maher, Chuck Liddell, Chris Rock, Orlando Bloom, Steven Spielberg, Paris Hilton, Katy Perry, Robin Thicke, Cara Delevingne, Dr. Dre, Anderson Paak, Tyga and Brad Pitt with girlfriend Ines de Ramon.

Leonardo's 81-year-old dad, George, also made a cameo with Leo's stepmom Peggy DiCaprio.

The main attraction -- Leo -- was laying low inside the house, but he couldn't escape our cameras. We captured the actor getting emotional as Stevie Wonder sang happy birthday to him. Leo's best friend, Tobey, was by his side to share the touching moment.

And Leo's better half, supermodel Vittoria Ceretti, gave him the biggest gift of all -- a nice kiss on the cheek.