The aim of this study is to examine the role of Dutch second grade (age 13-14) high school peer networks in mediating socioeconomic background and school type effects on smoking behavior. This study is based on a longitudinal design with two measurement waves at five different high schools, of the complete networks of second grader friendships, as well as their smoking behavior, school type, and parents' educational level. The analysis is done by simulation investigation for empirical network analysis (SIENA) modeling that can control for friendship selection on the basis of smoking similarity when assessing friends' influence on smoking. The findings show that, when controlling for friendship selection, the influence of friends still plays a significant role in adolescent smoking behavior, and suggests that socioeconomic background and school type effects on smoking are mediated by the friendship networks at school. (Contains 9 tables.)