This study examined whethera leisure focused intervention, HealthWise, was related to reduced youth polysubstance use and delayed sexual debut via reducing how often youth did leisure activitiesbecause there was nothing else to do. HealthWise was compared to a no-interventioncontrol for 5,610 high school students from 8 th to 10 th grade in townships near Cape Town, South Africa. Three specific leisure activities were examined: time spent with friends, playing sports, and going to parks. Among girls, time spent with friends because there was nothing else to do significantly mediated the effect of HealthWise on reducing frequent polysubstance use in the past month. For boys, time spent in parks because there was nothing else to do mediatedthe effect of HealthWise on delayed sexual debut. Results partially supported the HealthWise logic model of impacting risky behaviors via leisure and the value of prevention programs addressing the reasons behind leisure choices.