Research in the area of social cognition has suggesed that actual stimuli don't predict later judgments and responses as well as cognitive representations of and cognitive responses to those stimuli, in the form of attitudes, impressions, or causal attributions. To identify the factors most important in predicting adolescent smoking, a 4-year longitudinal study was conducted using a sample of students in grades 6 through 12. Three major categories of factors were used: (1) proximal variables (attitudes, beliefs, intentions) from Ajzen and Fishbein's (1970) model of behavior prediction; (2) general personality and perceived environment factors from Jessor and Jessor's (1977) problem behavior theory; and (3) perceived smoking environment factors. These factors were assessed across sex, age, and stage of smoking. The results supported the utility of a cognitive social-psychological approach to understanding adolescent smoking behavior. For adolescents who had already experimented with cigarettes, increases to regular smoking were best predicted by attitudes and beliefs about smoking as well as behavioral intentions to smoke (i.e., the Ajzen and Fishbein variables). Those who tried smoking but did not become regular smokers placed higher values on independence and had higher expectations for actually attaining independence, which may have helped reduce peer influence. In contrast, initial experience with smoking was more dependent on the immediate situational context. Moreover, adolescents grossly overestimated the actual extent of smoking among adults and teenagers. Self-image and social image were also related to adolescents' smoking decisions. The findings should prove useful in designing more effective interventions for primary prevention of smoking among adolescents. (JAC)