Stephanie Pratt was arrested for suspicion of driving under the influence at 3:45 a.m. Sunday in Hollywood.
Pratt, 23, was released on $5,000 bail late Sunday morning. Her booking info reveals the 5'7" reality star weighs 115 lbs.
Pratt had been partying at Holly Montag's birthday bash at Los Angeles club Empire earlier that night. At 11 p.m., she Twittered: "its my sissy @hollymontags bday party! just finished dinner and going to Empire but im pretty tired aka yes i am the party pooper :("
TMZ.com first reported the arrest.
Pratt has admitted to having an addiction to drugs and alcohol. She recently opened up to Us Weekly about her battle with bulimia.
"The more I can stress about being honest, [the better]," she told Us. "You are as healthy as your secrets."