Aims: Most national drug policies target both the supply side and the demand side of illicit drug use. Although such policies are intended to affect individual choices, they by definition operate on a national level and cannot be evaluated solely on the basis of individual-level differences. This study aims to evaluate the impact of country-level differences in the availability and perceived risk of cannabis use on individual-level adolescent cannabis use. Method: The study is based on an analysis of 84,711 students in 31 European countries. Multilevel modelling techniques are used to estimate the effects of country-level differences in the perceptions of availability and risk among non-users on individual-level odds of 30-day cannabis use. Findings: On the individual level, adolescents who use cannabis find it easier to obtain and less risky if they have used the drug. Controlling for these individual-level associations, adolescents are also found to be less likely to use cannabis in countries where non-users report less availability and more risks associated with cannabis use. Conclusions: These findings support the notion that both supply reduction and demand reduction may reduce the prevalence of adolescent substance use. (Contains 2 tables.)