Background: Over the years, the closure of institutions has meant that individuals with intellectual disabilities (IDs) must access mainstream (i.e. general) mental health services. However, concern that general services may not adequately meet the needs of patients with ID and mental illness has led to the development and implementation of more specialised programmes. This study compares patients with ID receiving specialised services to patients with ID receiving general services in Ontario's tertiary mental healthcare system in terms of demographics, symptom profile, strengths and resources and clinical service needs. Method: A secondary analysis of Colorado Client Assessment Record data collected from all tertiary psychiatric hospitals in the province was completed for all 371 inpatients with ID, from both specialised and general programmes. Results: Inpatients in specialised programmes were more likely to have a diagnosis of mood disorder and were less likely to have a substance abuse or psychotic disorder. Individuals receiving specialised services had higher ratings of challenging behaviour than those in more general programmes. The two groups did not differ significantly in terms of recommended level of care, although more inpatients from specialised programmes were rated as requiring Level 4 care than inpatients from general programmes. Conclusions: In Ontario, inpatients in specialised and general programmes have similar overall levels of need but unique clinical profiles that should be taken into consideration when designing interventions for them.