The group performed a nine-song set at a party fundraiser for Flea's Silver Lake Conservatory music school in Los Angeles.
Before hitting the stage on his doorstep, the thrilled bassist told Rolling Stone, "For this to happen on my 50th birthday tonight is the best gift I could ever hope to receive.
"A big part of my life is music education because it changed my life... I always think of this one kid that I taught for a while, bounced around from foster home to foster home and institutions and was so troubled. I would go to see him in places where he lived in these institutions and it was rough, hard to come out of that. (But) he loved it and now he's at Usc (University of Southern California), thriving."
The Red Hot Chili Peppers weren't the only band on the birthday bill - punk icons Rancid opened for them.
Frontman Tim Armstrong had a very special reason to be there - he attended the Silver Lake Conservatory as a student.
Flea revealed, "He took lessons there - he was taking flamenco or something. Tim's cool (and) those guys showed up. They played for us before, paid for everything, gave us all the merch (merchandise), everything. Those guys are so generous."
Singer/songwriter Ben Harper was also a special guest, performing a Happy Birthday-infused rendition of Leonard Cohen's Hallelujah.
And artists Banksy and Takashi Murakami donated original pieces of art for a backyard auction, which raised hundreds of thousands of dollars for the birthday boy's music school.
Guests at the party included actors Owen Wilson and Ed Norton.