Adolescent risk behaviours, such as violence and substance use, are prevalent public health concerns in Canada. Further, these behaviours often co-occur, and are associated with poor mental health. However, the majority of prevention programs focus on preventing single issues and do not consider mental health, and also neglect the importance of relationships when promoting positive youth development. To address this gap, the Centre for Addiction and Mental Health (CAMH) Centre for Prevention Science designed the Fourth R Healthy Relationships Plus Program, a small group program focused on the promotion of positive mental health and the reduction of violence and substance use, via the development of improved communication, interpersonal and help-seeking skills. The purpose of this study is to evaluate the Fourth R Healthy Relationships Plus program using both outcome (randomized controlled trial design with follow-up at pre-test, post-test, and 4, 8 and 12 months) and process evaluation tools.