Purpose:To evaluate the impact of an intervention designed to facilitate co-production on the client-therapist therapeutic relationship in an intellectual disability service.Design:The ‘My Psychology Treatment Plans’ intervention was administered to 20 service users during their first three months of admission to a tier four specialist intellectual disability forensic service. Pre- and post-scores were collected using the service user version of the Scale to Assess Therapeutic Relationships (STAR-P; McGuire-Snieckus et al., 2007).Findings:A paired-samples t-test revealed a significant increase in positive collaboration, positive clinician input, and overall total score. This suggested an overall increase in positive therapeutic relationship.Practical implications:The findings support the existing literature of the importance of co-production in increasing the therapeutic relationship between client and therapist, and co-production should be a key component of developing treatment plans.Originality/value:This study contributes to developing an understanding of the importance of co-production in secure services, particularly within an intellectual disability population.