Schools differ in the proportion of their pupils who smoke. Such differences transcend pupil intake characteristics and relate to the internal life of the school. Although adolescents' smoking behaviour has been associated with that of their peers, little consideration has been given to whether peer structures and processes contribute to school differences in pupil smoking rates. In two relatively deprived Scottish schools, one with a higher and one with a lower rate of pupil smoking, 13 and 15 year-olds were surveyed. Sociometric data and information on pupils' smoking behaviour and views were gathered. Twenty-five single-sex discussion groups were then held with a sub-sample of the 13 year-olds in order to explore in detail their views on smoking, smokers and fellow pupils. Findings showed that in the higher smoking school, pupils were more often in groups, smokers were identified as popular, and attitudes (especially among non-smoking females) were more pro-smoking. In the lower smoking school, by contrast, there were more isolates and dyads, there were no popular smokers and attitudes (especially among non-smoking females) were much less pro-smoking. Thus, evidence suggests peer group structures and related influences could be one explanation for school differences in smoking, and that the popularity of smokers together with the views of non-smoking females may be particularly important in creating such differences.