Objective: This article identifies behavioral trajectories of American Indian adolescents and examines their predictors. Method: A total of 401 urban and reservation American Indian adolescents were interviewed yearly from 2001 to 2004 (with 341 youths, or 85%, retained to 2004, and 385 completing at least two interviews). The Youth Self-Report total problem score is used to model behavior change trajectories, with psychological (addictions and mental health) and environmental (family, peer, community, and services) variables as independent variables. Analyses were based on PROC TRAJ, an SAS macro. Results: Five trajectory groups were found. Youths who started with a Youth Self-Report score less than the clinical cutoff were low stable (n = 142) or low improving (n = 175). Youths with initial scores over the cutoff were very high chronic (n = 5), high improving (n = 30), or high chronic (n = 33). High improvers scored close to the low improving group by 2004. At baseline, the high improving group was more likely than the high chronic group to be from the reservation (odds ratio 5.94), have greater family satisfaction (1.14), and have fewer school problems (0.84). Over time, the high improving group had substance use and depression drop, family satisfaction increase, fewer parents with mental health or addictions problems, fewer peers using substances, and a decrease in neighborhood problems and stressors. Conclusions: A significant majority (more than 82%) of the youths exhibited relatively low levels of problem behaviors over all 4 years, and 42% of those with clinically significant problems improved over time. (Contains 5 tables and 1 figure.)