This study attempts to evaluate the relative impacts of parents, siblings, and classmates on youth smoking by employing longitudinal data from the Waterloo Smoking Prevention Program (WSPP), a chronicle of smoking habits of students enrolled in various high schools in South Western Ontario, between 1993 and 1996. The empirical results reveal household and classmate smoking to be significant determinants of individual smoking participation as well as daily smoking. Specifically, an increase in the proportion of classmates who admit to smoking and cigarette consumption by an elder sibling, are both significantly correlated with a higher probability of youth smoking. This is a consistent finding across OLS, within-individual, and IV estimates. Finally, simple OLS estimates suggest the presence of non-linear effects with respect to classmate smoking.