The sample included 1,766 American Indian adolescents from three culture groups who provided repeated measures of 30-day marijuana use twice a year across a 3-year period. Linking five age cohorts, hierarchical linear modeling was used to model a curvilinear trajectory of marijuana use. Gender and community differences were also examined. Findings revealed support for a maturational model of marijuana use across time. Marijuana use increased in middle adolescence, peaked in later adolescence, and began to decrease in early adulthood. Both gender and community differences in marijuana use trajectories were significant. The authors conclude that marijuana use among American Indian adolescents follows a clear developmental trajectory and that growth curve analysis can provide an additional tool for studying the effects of interventions that may not be apparent in a traditional evaluation design. 30 references, 1 table, and 1 figure