The primary aim of this study was to determine the clinical factors differentiating adolescents with heavy smoking (> or = 10 cigarettes/day) from adolescents with light smoking. This study involved a study group of 812 adolescents recruited from adolescent alcoholism treatment centers and from the community. Logistic regression analyses demonstrated that adolescents with heavy smoking, compared with adolescents with light smoking, were significantly more likely to demonstrate Caucasian American ethnicity, drug-use disorders, alcohol-use disorders, and conduct disorder. Our findings suggest that the clinical correlates of heavy smoking among adolescents are generally similar to those for smoking at any level (vs. nonsmokers), except that heavy smoking is more strongly associated with Caucasian American ethnicity. Also, depressive disorders were associated with smoking at any level in our sample, but depressive disorders were not associated with heavy smoking.