Background: There are a variety of models for the mental health care of adults with comorbid intellectual disability (ID) and mental illness. There has been a long-running debate as to whether this should be provided by general psychiatric or specialised ID services. A previous review concluded that there was no clear evidence to support either model with research being often of a poor quality, lacking replication, and outcome measures were often inappropriate or varied between studies. This review aims assess differences in outcome for patients with ID and mental disorders treated in general or specialised ID mental health services. Method: A literature review was conducted using electronic databases and websites of ID and mental health organisations to locate all references where people with ID receive mental health care in general psychiatric services from 2003. No meta-analysis was attempted because of the divergent nature of the studies. Results: People with ID (especially severe ID) have reduced access to general psychiatric services. General psychiatric inpatient care is unpopular especially with carers but can be improved by providing specially trained staff and in-reach from community ID teams. Opportunities may exist to enhance the care of people with borderline intellectual functioning within general psychiatric services. Conclusions: Although no new randomised controlled trials have been published, the weight of research is accumulating to suggest that provision of general psychiatric services without extra help is not sufficient to meet the needs of people with ID.