Primary prevention of smoking in adolescents requires effective screening instruments for identifying those adolescents who are most likely to experiment with cigarettes. This study investigated the predictive value of a measure of susceptibility to smoking (the lack of a firm commitment not to smoke) for predicting smoking initiation 1 and 2 years later among 687 seventh-grade nonsmokers. Results showed that susceptible adolescents were approximately two to three times more likely to experiment with cigarettes during the ensuing 2 years than were nonsusceptible adolescents. At the lower levels of smoking, these relationships persisted even after controlling for psychosocial variables. Measures of susceptibility to smoking could be an effective tool for identifying adolescents at increased risk of experimenting with cigarettes or assessing their readiness for smoking-prevention programs.