War veterans experience psychological disorders as a result of deployment. Peer outdoor support therapy (POST) may be an alternative or complementary therapy, as part of the larger field of complementary and alternative medicine (CAM), to traditional psychological approaches for the treatment of psychological disorders arising from deployment. The long-term benefit of Trojan’s Trek, an Australian POST, was evaluated for its benefits on wellbeing, depression, anxiety, and stress. Nine male participants who participated in Trojan’s Trek during 2013 completed four self-report questionnaires across four time-points, as follows: General Perceived Self-Efficacy Scale (GSE), Life Satisfaction Questions (LSQ), Positive and Negative Interactions Scale (PNI), and Depression Anxiety Stress Scales short-version (DASS-21). Questionnaires were administered pre-Trek, immediately post-Trek, at 2-3-month follow-up, and 9-month follow-up. The resultant data were analyzed using Reliable Change Indexes (RCI). Depression, anxiety, and stress decreased, and wellbeing increased, post-trek. Reliable decreases for depression, anxiety and stress, and reliable increases in Self-Efficacy were observed post-trek. Positive outcomes for participants were achieved immediately post-Trek and over a nine-month period. POST may supplement current empirically supported psychological treatments for psychological disorders arising from deployment.