To examine how older smoking peers at school and the smoking behavior of friends and family members are related to youth smoking. The School Smoking Profile was used to collect data on tobacco use and determinants of tobacco use from 22,091 students from 29 secondary schools in Ontario, Canada. Correlates of occasional and regular smoking were examined using multilevel logistic regression analyses. Students are at increased risk for smoking if they (a) have smoking friends, (b) have smoking family members, and (c) attend a school with a relatively high senior-student smoking rate. These findings suggest that prevention programs should target both at-risk schools and at-risk students.