The impact of group identity on adolescent tobacco, alcohol, and marijuana use was examined through a postal survey. The study included adolescents who identified with 1 subgroup (n = 1425) as well as adolescents who identified with 2 (n = 895) or 3 (n = 339) subgroups. The results showed that identification with the pop, skate/hip-hop, techno, and hippie subgroups was associated with higher risks of substance use, whereas identification with the sporty, quiet, computer nerd, and religious subgroups was associated with lower risks. Perceived group norm mediated the group identity-substance use relationship. Furthermore, identification with multiple groups with corresponding norm increased norm-consistent substance use, whereas identification with multiple groups with opposing norms reduced normative behavior. Implications for health promotion are discussed.