Outcome expectancies have been related to smoking behavior among adults, but less attention has been given to expectancies about smoking among adolescents at differing levels of smoking experience. The present study reports the psychometric properties and predictive validity of a brief expectancy scale across two samples of adolescents. Sample 1 (N = 349) consisted of high school students (54% female) who were regular smokers enrolled in a cessation program. Sample 2 (N = 273) consisted of 8th- and 10th-grade early experimenters (54% female) involved in a natural history study of smoking trajectories. In both samples, a principal component analysis of a 13-item expectancy scale yielded four factors (taste, weight control, boredom relief, and negative affect management), each with high internal consistency (coefficient alphas >.77) and accounting for 73% and 80% of the total variance for each sample, respectively. Expectancies were significantly higher among current smokers than among early initiators. In Sample 1, boredom relief and weight management expectancies predicted smoking status 6 months later. In Sample 2, students whose smoking increased over 18 months had higher overall expectancies at baseline compared with those who tried smoking and did not escalate. These findings support the predictive validity of expectancies in predicting escalation and cessation. Implications for the importance of expectancies in understanding adolescent smoking behavior are considered.