Maggie & Jake Gy...Actors Maggie and Jake Gyllenhaal. (Photo by Pascal Le Segretain/Getty Images)
Shirley MacLaine...Actors and siblings Shirley MacLaine and Warren Beatty. (Photo by Kevin Winter/Getty Images for AFI)
The PhoenixesJoaquin Phoenix and his sister Rain Phoenix. (AP Photo/Carolyn Kaster)
River PhoenixTheir brother, actor River Phoenix, passed away in 1993.(Photo: MPTV)
Rob & Chad LoweRob and Chad Lowe with their mother Barbara. Photo by Kevin Winter/Getty Images.
Shawn, Kim & Kee...Actors Shawn, Kim and Keenan Ivory Wayans. (Photo: Scott Gries/ImageDirect)
Garry & Penny Ma...Directors Garry Marshall and Penny Marshall. (Photo by Matthew Simmons/Getty Images)
Luke & Owen Wils...Luke Wilson and his brother, actor Owen Wilson. (Photo by Vince Bucci/Getty Images)
Ben & Casey Affl...Actor/director Ben Affleck and his brother actor Casey Affleck. (Photo by Claire Greenway/Getty Images)
Ralph & Joseph F...Actors and brothers Ralph Fiennes (L) and Joseph Fiennes. (Photo by Claire Greenway/Getty Images)
John &Joan Cusac...Siblings (L-R) Ann, John, and Joan Cusack. (Photo by Matt Carmichael/Getty Images)
The ArquettesActors Thomas Jane, Patricia Arquette, Roseanna Arquette, Alexis Arquette, Richmond Arquette, David Arquette and his wife Courteney Cox Arquette. (Photo by Kevin Winter/Getty Images for AFI)
Ashley & Mary-Ka...Actors Ashley Olsen and Mary-Kate Olsen. (Photo by Rob Loud/Getty Images for IMG)
The Smothers Bro...Comic actors and musicians Tommy Smothers (L) and Dick Smothers. (Photo by Frederick M. Brown/Getty Images)
Alec & Stephen B...Actors Alec Baldwin (L) and Stephen Baldwin. They also have two other brothers... (Photo by Bryan Bedder/Getty Images)
Billy & Daniel B......who are also actors: Billy (L) and Daniel Baldwin. (Photo by Frederick M. Brown/Getty Images)
Elizabeth & Andr...Elizabeth Shue and brother actor/producer Andrew Shue. (Photo by Alberto E. Rodriguez/Getty Images)
Dennis & Randy Q...Actors Dennis Quaid and Randy Quaid. (Photos by Getty Images)
Jessica & Ashlee...Singers and songstresses Jessica and Ashlee Simpson. (AP Photo/Alan Diaz)
Donny & Marie Os...Brother and sister entertainers Donny and Marie Osmond. (AP Photo/Eric Jamison, file)
Britney & Jamie ...Singer Britney Spears and her sister, actress Jamie Lynn Spears. (Photo by Frank Micelotta/Getty Images)
Hilary & Haylie ...Actress Haylie Duff and her singer/actress sister Hilary. (AP Photo/Stuart Ramson)
The Jonas Brothe...From left, teen heartthrob musicians and brothers Nick, Joe and Kevin Jonas. (Photo by Scott Gries/Getty Images)
Celebrity Sister...You've seen famous siblings, but do you know all of Hollywood's famous little sisters? To see them, click here.