Background: The purpose of this paper is to describe long-term outcomes for patients discharged over a 12-year period from a medium secure service for people with intellectual disabilities (ID). Methods: A cohort study using case-notes analysis and a structured interview of current key informants. Results: Eleven per cent of the sample was reconvicted. Fifty-eight per cent of the sample showed offending-like behaviour that did not lead to police contact. Twenty-eight per cent of the sample was currently detained in hospital under the Mental Health Act. The presence of a personality disorder, a history of theft or burglary, and young age increased the risk of reconviction. Contact with the police was less likely in those with schizophrenia. Re-admission to hospital was associated with the presence of offending-like behaviours, rather than any specific diagnosis. Conclusion: In terms of reconviction, these results are good compared with those from general forensic services; however, behavioural problems continue for many years and are managed without recourse to the criminal justice system. There is a borderline group whose needs are poorly defined and serviced.