Data regarding lifetime, 90 days prior to treatment, and 1-year posttreatment substance use were collected using interviews, questionnaires, and observations of 57 American Indian adolescents and their families. Trajectories of days-used measures were subjected to semiparametric trajectory analysis. Trajectories were then compared on baseline measures by using both univariate and multivariate logit regression techniques. The study sought to identify prerelease predictors of membership in post-inpatient treatment substance use trajectory groups. Findings provide insight into the unique and shared risk and protective factors relevant to American Indian adolescents' substance use outcomes. In particular, this study suggests that a combination of family management and American Indian traditional cultural practices in families serves as a potential target for interventions to reduce substance use in adolescence. (Published Abstract)