This article describes the issues associated with the development of services for people with intellectual disabilities (ID) and mental disorders [including challenging behavior (CB)] and reviews the evidence for providing effective community mental health services.Despite the fact that deinstitutionalization has been on the forefront of policies to improve social care for individuals with ID in the community, there has not been an equivalent drive to offer appropriate and effective interventions for the treatment of mental illness in this population. Evidence-based practice is still in its infancy and mental health outcomes are just beginning to emerge. The mental health component of existing specialist services is not fully integrated in many localities and mental health input is even considered stigmatizing to people with ID. Yet, people with ID have a higher prevalence of mental disorders, including schizophrenia and CB, and are vulnerable to overmedication and abuse. Furthermore, there has been more research on service models for CB than for mental health services. However, there is a need for further investigations of outcomes and of the application of such well known examples of community care as assertive community treatment, intensive case management and crisis resolution. People with ID deserve robust services to manage mental illness in this population.