The Childhood Antecedents of Smoking Study (CASS) investigated patterns of cigarette smoking among junior and senior high school students in an upper midwest school district. Four biannual school-based surveys were conducted over two years. A cohort of 72 smokers was identified and followed to determine who continued smoking and who quit. Discriminant analysis was used to study social, psychological, and environmental factors predictive of quitting smoking. Compared to continuing smokers, quitters reported having fewer friends and siblings who smoked, they were less likely to view the cigarette smoker's image as positive, and lived in families where parental involvement with teenagers was high (based on the reports of parents). These results are consistent with the view that social influences are strong determinants of patterns of adolescent smoking behaviour.