Longitudinal studies have consistently found that adolescents whose friends smoke are more likely to smoke themselves (e.g., Chassin, et al., 1991; Cohen, et al., 1994; Jackson, et al., 1998; Wang, et al., 1999). There has been some debate, however, about whether having smoking peers actually encourages a teenager to initiate smoking (influence) or whether adolescents who smoke simply choose friends who share their smoking behavior (selection). While it is likely that selection plays a role, recent evidence suggests that the smoking habits of peers do influence a teenager's likelihood of smoking (Wills & Cleary, 1999). This finding was based on a two-year follow-up of a sample of nearly 2,500 urban and suburban 6th and 7th graders, who were 37% white, 29% African American, 23% Hispanic, 3% Asian American, 5% other ethnicity, and 3% mixed ethnicity. The reason behind the relationship between peer and adolescent smoking has not been established, but it is possible that peer smoking affects smoking risk via peer pressure, modeling, social reward or approval, or some combination of these or other mechanisms (Rowe, Chassin, Presson, Edwards, & Sherman, 1992). Indeed, additional longitudinal research (MacKinnon, et al., 1991), including one study based on a nationally representative sample of initially non-smoking adolescents (Wang, et al., 1999), has suggested that perceived peer approval of smoking behavior is predictive of adolescent smoking.

Peers also serve as a primary source of cigarettes. In a survey of 7th graders in a large, urban, primarily black school system, Robinson, Klesges, and Zbikowski (1998) reported that peers were the most common single source of cigarettes for both experimental and regular smokers, with 28.4% of experimental and 57.0% of regular smokers listing peers as a cigarette source.