Background: In forensic settings, patients with intellectual disabilities are overrepresented. A relative novel treatment approach for this population is schema therapy. The goals of schema therapy for offenders with intellectual disabilities are to reduce maladaptive emotional states and to reinforce healthy emotional states and enhancing the patient's ability to ask for help. No studies are examining the effectiveness of this approach. Method: We examined the effectiveness of Schema Therapy for offenders with intellectual disabilities (ST-ID) in terms of emotional states, psychological complaints, and violence risk in six participants. Results: Reliable change analyses showed significant improvements in emotional states and certain psychological complaints. Conclusions: While many questions remain about the effectiveness of ST-ID, our study shows that offenders with ID can benefit from this psychological treatment.