Alessandra Ambrosio was decked out in a Black Swan look for a party at the Roosevelt Hotel in LA
Ali Larter and Hayes MacArthur were bumble bees on Saturday night
Gwen Stefani dressed up as Cinderella for Kate Hudson's LA bash on Saturday.
Rashida Jones accessorized her Blow Pop costume with a lollipop.
Jamie Lee Curtis wore a Red Riding Hood outfit to the annual Dream Halloween charity event in LA on Saturday.
Bethenny Frankel donned Hello Kitty gear for Heidi Klum's Las Vegas party on Saturday.
Nicole Richie channeled Jennifer Lopez at Kate Hudson's party in LA Saturday.
Rose McGowan went back in time with her Halloween getup at a party in LA Friday nigh
's Alan Cumming wore a monkey suit to Bette Midler's annual party in NYC.
Debra Messing and Daniel Zelman painted their faces for Bette Midler's annual New York Restoration Project's Hulaween event.
Jerry Ferrara mixed up his Robin Hood outfit with a Yankees hat and headphones in LA on Friday.
Holly Madison wore a sexy costume to her annual "Hollyween" party at the MGM Grand in Las Vegas on Saturday.
Melissa Rycroft and her husband Tye Strickland dressed up as The Flinstones with their daughter Ava for the Dream Halloween charity event in LA.
Judd Apatow and Leslie man went 80s for a party in LA Saturday.
Lance Bass rocked a crazy costume at an LA party on Friday.
( I don't get it and I don't like it!)
NBA star Carmelo Anthony got into ganstar gear for Bette Midler's Halloween bash at the Waldorf-Astoria.
Kim Kardashian was a sexy Poison Ivy at an NYC bash on Saturday.
At a friend's LA party, Nicky Hilton put on her best sexy cat costume.
Eli Roth and a pal checked out a house party in LA on Friday.
Zooey Deschanel dressed up as Adele for Kate Hudson's party in LA.
David Arquette dressed up for a friend's party in Beverly Hills on Friday.
Designer Michael Kors went with a mariachi look at Bette Midler's NYC party.
Bette Midler had Stevie Wonder by her side at her 16th annual New York Restoration Project's Hulaween in NYC on Friday.
Chef Sandra Lee channeled a princess at Bette Midler's annual Halloween party at the Waldorf-Astoria.
Angel, Rachel, and AnnaLynne McCord stuck together at Pure Nightclub's party in Las Vegas Friday.
Heidi Klum rolled into her Las Vegas party in an anatomically correct "Visible Woman" costume.
Katie Couric dressed up for an '80s concert in NYC.
Camille Grammer got into the spirit at LA's annual Dream Halloween charity event on Saturday.
David Arquette dressed up as Elvis for Kate Hudson's Halloween bash in LA on Saturday.
Scott Disick was a priest for Halloween in Las Vegas.