Background: Mental health services for patients intellectual disabilities (ID) and additional mental illnesses are only sparsely studied. Objective: The objective was to describe a representative sample of patients with ID in a specialized psychiatric department. Methods: Data were collected from case files in a 7-year period. Of 143 invited patients, 133 participated. Results: More than 60% were admitted involuntarily. Schizophrenia was found in 30.1%, mood disorder in 25.6%, and anxiety disorders in 15.8%, Obsessive Compulsive Disorder (OCD) in 8.4% and Post Traumatic Stress Disorder (PSTD) in 12.9%, PD in 14.3%, and ADHD in 12%. Average waiting time was 6.1 months. Length of stay was 9.1 months for the inpatients. Conclusion: Services for patients with ID appear to still be reliant on inpatient units for at least a proportion of their patients. More research is needed to find out why this is. The results raise questions about referring, compliance between psychiatric diagnosis, and interventions.