Parental monitoring is commonly accredited as an important protective factor against risky adolescent behaviors. In this meta-analytic review, associations of adolescents' perceptions of parental monitoring with adolescent marijuana use were collected and quantified across 25 independent samples from 17 empirical studies involving 35,367 unique participants. Applying a random-effects model, the average magnitude of effect was r = -.21,. The association was significantly stronger in female-only samples (r = -.31 vs. r = -.19, p < .001) and when parental monitoring was defined purely in terms of parental knowledge of the child's whereabouts, activities, and relations (r = -.24 vs. r = -.19, p < .05). Cross-sectional (r = -.23) and longitudinal studies (r = -.10) disclosed significant effect sizes. To assess publication bias, a file-drawer analysis indicated that 7,358 studies of nil effect size would be necessary to render the association of parental monitoring and reduced marijuana usage nonsignificant. Theoretical and practical implications of parental monitoring are discussed, especially issues concerning the measurement of parental monitoring and the possible utility of the construct in curtailing marijuana use.