BACKGROUND Previous research has shown that meanings of smoking are highly predictive of smoking in middle school children. Three factors of meanings of smoking have been suggested in the literature: personal meanings, functional meanings, and social meanings. These conceptually derived factors of meanings of smoking have not previously been empirically studied. PURPOSE This study examined the factor structure of the Meanings of Smoking Index (MSI) to determine the unique contribution of meanings of smoking and positive outcome expectancies to smoking behavior in middle school children. METHODS A multiethnic sample of 2,247 eighth-grade students enrolled in 24 middle schools in greater Los Angeles completed a paper-and-pencil survey in class. RESULTS Four factors of the MSI emerged (functional, personal, social image, and weight concern). Positive outcome expectancies and each of the four factors of the MSI predicted lifetime smoking in a multivariate model. CONCLUSIONS Meanings of smoking were empirically distinct from positive outcome expectancies. Adolescents who endorsed personal and functional meanings were more likely to smoke. Social image and weight concern meanings were negatively related to smoking after controlling for all other meanings. Meanings of smoking may prove to be important and modifiable mediators of smoking and therefore useful in future prevention studies.