The Health Behavior in School-Aged Children Study has been an important source of international comparisons on the health and welfare of children. In this study of more than 93 000 15-year-olds, cannabis use in the prior 12 months was strongly associated with the frequency of spending evenings out with friends in both boys and girls. Reported cannabis use decreased in most of the countries between 2002 and 2006, and changes in the mean frequency of going out with friends were strongly linked to changes in the prevalence of cannabis use. Canada, Switzerland, and the United States remained the countries with the highest prevalence of cannabis use in 15-year-olds. The findings are consistent with the hypothesis that by going out less frequently at night with friends, adolescents had fewer opportunities to obtain and use cannabis. It is important to determine how to foster opportunities for social interactions among youth that do not provide exposure to substance use.