Therapeutic community treatment models have not previously been applied to forensic patients with mild intellectual disabilities (IDs) with a comorbid diagnosis of personality disorder. Thirteen patients with mild IDs were allocated to a unit within a high secure psychiatric service operating a model of treatment based on the principles and practices of therapeutic communities. After 2 years, 9 patients remained in treatment. Self-rated personality disorder traits, maladaptive schema relating to personality disorder, and clinician-rated psychopathy were measured at start of treatment and after 2 years. Seclusion hours were measured for 6 months before treatment and during the 2 years of treatment. There were significant reductions in antisocial, schizoid and paranoid traits, and in schemas relating to entitlement, defectiveness, emotional inhibition, and vulnerability. There were no changes in ratings of psychopathic traits. Mean seclusion hours had reduced by over 90% in the latter 6 months of treatment compared with the 6 months before treatment. The results provide encouraging support for a therapeutic community approach for some individuals with mild IDs and personality disorder diagnoses and are discussed in the light of the severe pathology of the patients undergoing treatment. Therapeutic community approaches are nevertheless consistent with the move toward greater patient involvement in services and treatment.