Aggression in young people has been associated with a bias toward attributing hostile intent to others. However, little is known about the origin of biased social information processing. The current study explored the potential role of peer contagion in the emergence of hostile attribution in adolescents. One hundred thirty-four adolescents (M age = 13.8 years) were assigned to one of two manipulated "chat-room" conditions, where they believed they were communicating with online peers (e-confederates) who endorsed either hostile or benign intent attributions. Adolescents showed increased hostile attributions following exposure to hostile e-confederates and reduced hostility in the benign condition. Further analyses demonstrated that social anxiety was associated with a reduced tendency to take on hostile peer attitudes. Neither gender nor levels of aggression influenced individual susceptibility to peer influence, but aggressive adolescents reported greater affinity with hostile e-confederates. (Contains 1 table and 1 figure.)