This study aimed to compare the characteristics of service users with intellectual disabilities and mental health problems admitted to either a specialist or a generic inpatient unit in an area of South London. Socio-demographic and clinical characteristics of consecutive admissions over a 5.5-year period were recorded using a questionnaire. Key differences in psychiatric diagnosis, residence type and discharge destination were found between individuals using generic and specialist provision. Length of stay was significantly longer for specialist unit admissions. Admissions to the specialist unit were significantly more likely to reside with family prior to admission and admissions to generic units were significantly more likely to come from "other" forms of residence such as hostels, prison and "no fixed abode". At discharge the proportion of those admitted to the specialist unit who resided with their families reduced. At the same time the proportion of those living in supported accommodation increased although compared with those admitted to generic units they were still significantly more likely to return to the family home. Significantly, more adults admitted to generic units were diagnosed with an affective disorder. Specialist inpatient provision may be crucial in helping mainstream services meet the needs of individuals with intellectual disabilities and mental health problems.