Kim Kardashian
The Keeping Up With the Kardashians star celebrated her 29th birthday at Tao nightclub in Sin City. Boyfriend Reggie Bush couldn't make the bash, but she flew to see him in New Orleans the next day.
Ashlee Simpson
Ash celebrates turning 25 with help from sister Jessica Simpson at Wet Republic. Hubby Pete Wentz was also there for the pool party.
Lindsay Lohan
Can you believe LiLo is only 23? The actress showed up to the shindig at Wet Republic sans Sam Ronson.
Lauren Conrad
The Hills star heads to Vegas for her 23rd! L.C. had dinner with boyfriend Kyle Howard and friends at Lavo before heading over to Tao for more fun.
Jennifer Aniston
Ellen DeGeneres presented Jen with a cake to commemorate her 40th birthday in February. On the guest list for the bash held at Aniston's Beverly Hills home? John Mayer, Oprah Winfrey and E!'s own Chelsea Handler.
Selena Gomez
The Disney darling had to shoot her show, Wizards of Waverly Place, on her 17th birthday, but was brought to tears by the gifts from fans and friends, including flowers, a pop-up card and an apron!
Rumer Willis
Demi Moore and Bruce Willis' oldest daughter turned 21 in style with a Sin City soiree at Tao. Her famous folks and stepdad Ashton Kutcher were there to celebrate, along with an Elvis impersonator.
Nick Cannon
Mariah Carey helps her hubby turn 29 at the Bank nightclub in Vegas, where she presented him with a cake reading "Happy Birthday DJ Sexy Fingers." The nimble-fingered birthday boy also worked the turntables at his bash.
Cara & Mady Gosselin
Father of the Year Jon Gosselin picks up a misspelled cake at a New York bakery before heading back to Pennsylvania for his twins' ninth birthday party.
Jennifer Lopez
J. Lo gets surprised with a huge chocolate cake from the cast and crew of The Back-Up Plan in the Big Apple. Can you believe Jenny's 40?
Madonna
Madonna's secret to staying young? Having a 23-year-old boy-toy! The 51-year-old celebrated her most recent milestone with an Italian pleasure cruise with kids and boyfriend, Jesus Luz, in tow.
Giuliana Rancic
The E! News host is joined by her hubby, Bill Rancic, for her birthday bash at Tabú lounge in Las Vegas.
See other stars get the party started in our Party Pics: Hollywood gallery!