Outdoor behavioral healthcare is an increasingly popular treatment modality for adolescents, and evidence suggests that it is effective for a wide range of complex issues. The outdoor behavioral healthcare literature still faces major limitations though, and one of these limitations is that outcomes are primarily measured at only admit and discharge. This study sought to explore the trajectory of change throughout treatment, and investigate outcomes up to 18 months post-discharge. Of the 659 adolescent participants from four outdoor behavioral healthcare programs, 29 % were female, 18 % were adopted, and the average age was 16 years old. Participants were invited to complete questionnaires four times during treatment, and at 6 and 18 months post-discharge. We used multilevel modeling to explore trajectories and predictors of change during treatment, and a regression and an ANOVA to examine outcomes post-discharge. Results of the multilevel modeling supported that adolescents make significant changes during outdoor behavioral healthcare, and also contributed new findings on demographic and diagnostic predictors. Gender and the presence of a mood or anxiety disorder predicted greater rates of change during treatment. Analysis of post-discharge data at six and 18 months post-discharge suggested that clients maintain treatment effects and that gender persists in influencing outcomes. This study is the first to examine trajectories of change in outdoor behavioral healthcare, to find diagnostic variables to be relevant, and to examine self-report outcomes past 12 months post-discharge.