Using a longitudinal design, the current study investigated the roles of smoking-related beliefs, and parent and peer psychosocial factors as antecedents and consequences of adolescent smoking cessation. Results indicated that adolescents who would later quit smoking were different from those who continued to smoke even prior to the transition. For younger subjects, cessation was related mainly to parental influences (e.g., parental support and attitudes towards smoking). Older adolescents responded primarily to peer influences in choosing to quit. While psychosocial factors served as antecedents to cessation, results also indicated that the process of quitting itself led to changes in the adolescents' social environment that further reinforced smoking cessation (e.g., fewer friends who smoked, less positive peer attitudes towards smoking). Thus, the process of smoking cessation among adolescents may be bidirectional, with psychosocial factors influencing the decision to quit and, in turn, being influenced by such a decision.