A sample of high school students in grade 9 and 13 (14-15 and 18-19 years old respectively) in Brescia, North Italy, were interviewed to assess the relationship of smoking habit with attitudes, knowledge, behavioural and socio-environmental factors among adolescents. The associations between smoking habit, considered as a dichotomous response variable, and the other variables were assessed by estimating the prevalence ratios. The following variables were found to be associated with the students' smoking: best friend and/or partner smoking, sibling smoking, alcohol drinking and the students' judgement of the health risks of smoking. Although no conclusion can be drawn on the causal relationship of these associations due to the cross-sectional design of the survey, these findings suggest that social environment influences adolescents' smoking more than family life does. Furthermore, the knowledge of the health risks of smoking was not associated to adolescents' smoking.