. In the longitudinal sample, greater knowledge of cigarette package warning labels was significantly associated with a subsequent increase in smoking, controlling for the baseline level of smoking, sex, ethnicity, and knowledge of warning labels on cigarette advertisements (odds ratio [OR], 1.22; 95% confidence interval [CI], 1.02-1.46). Knowledge of warning labels on cigarette advertisements was not associated with a significant change in smoking behavior (OR, 1.06; 95% CI, 0.82-1.35).