Surf therapy programs have been successfully utilised with vulnerable populations worldwide. This study is the first to examine the effects of a surf therapy program on the psychosocial functioning of young men at high risk of adverse life outcomes in Aotearoa New Zealand. A single-group pre-test post-test research design, with repeated measures and replication was used. The Youth Outcome Questionnaire Self-Report's Reliable Change Index and clinical cut-off scores were employed to assess outcomes pertaining to each individual. Effect size measures were used to estimate an overall treatment effect. Modified Brinley plots revealed that 25 out of 27 participants demonstrated reliable improvement in psychosocial functioning, 20 of whom also demonstrated clinically significant improvement. The effect size measures also confirmed a large overall treatment effect. Findings suggest that the Tai Watea surf therapy program may be a highly effective intervention for reaching, retaining and improving the psychosocial functioning of high-risk young men.