Background: Little is known about the effects of outdoor behavioral healthcare on participants' body composition or about the relationship between body changes and indicators of mental health. Purpose: The purpose of the current study was to compare body and mental health changes in adolescents in an 8-week adventure therapy program. Methodology/Approach: In this observational study, we analyzed pre- and posttest weight, body composition, and psychological dysfunction in male and female adolescent participants (N = 112) in an adventure therapy program. Body composition variables were assessed using bioelectrical impedance analysis. Psychological dysfunction was measured using the Youth Outcome Questionnaire (YOQ). We also analyzed the relationship between body changes and changes in YOQ scores. Findings/Conclusions: Overall, from entry into the program (pre) to time of discharge (post), body weight, BMI, and body fat percentage significantly decreased (ps [less than or equal to] 0.0014). Likewise, all YOQ variables significantly improved (scores reduced) over the course of the study (ps [less than or equal to] 0.0003). Changes in body composition and YOQ score were not associated. Implications: Adolescent participation in adventure therapy is significantly associated with improvements in BMI, body weight and composition, and psychological dysfunction. However, changes in body composition and psychological dysfunction do not appear to be associated.