Background: Psychiatric patients are more likely to be victims of crime than others in the community. Dual diagnosis patients with comorbid psychiatric and substance use disorders are especially prone to victimization. Victimization is associated with substance abuse, more severe symptomatology and homelessness. There is a strong need for interventions to reduce victimization in this population. We developed the Self-wise, Other-wise, Streetwise (SOS) training to reduce victimization in patients with dual diagnosis. Methods/design: This study is a randomized controlled trial using a parallel group design to determine the effectiveness of adding the SOS training to care as usual. Patients with dual diagnosis (N = 250) will be allocated to either care as usual plus SOS training (N = 125) or care as usual only (N = 125) using computer-generated stratified block randomization. To compare effectiveness participants will be interviewed at baseline and 2, 8 and 14 months follow-up. The primary outcome measure is treatment response (yes/no), defined as either no victimization at 14 months follow-up or at least a 50 % reduction in incidents of victimization at 14 months follow-up compared to baseline assessment. Victimization is measured with the Safety Monitor, an adequate self-report instrument used by Statistics Netherlands to measure victimization on a large scale in the Netherlands. Outcome assessors are blind to treatment allocation. An economic evaluation will be performed alongside the randomized controlled trial and will take the societal perspective. Discussion: This study is the first randomized controlled trial to examine the effectiveness of an intervention that aims to reduce victimization in patients with dual diagnosis. If the intervention is effective it can be implemented in mental health care and contribute to the safety and well-being of patients.