Background: This paper describes and appraises an inter-agency police liaison scheme for MDOs in Northern Ireland. Aims: To examine administrative outcomes and psychiatric assessment data (including some follow-up information) and to assess the views of service-users and key stakeholders. Method: A battery of measures was devised to assess mental health status, drug and alcohol abuse and risk-related behaviour. Outcomes were assessed (as far as possible) within a prospective follow-up design including a survey of service professionals and interviews with MDOs. The performance of the scheme was measured using objective indicators. Results: Ninety-one per cent of all assessed detainees (n = 382) were judged to have a mental health problem. Sixty-eight per cent were GHQ cases whilst 62% attained “above-threshold” BPRS scores; 48% and 53% respectively had a history of harming self or others. Improvements in mental health were recorded for MDOs who were linked to services and who could be followed up. The service was valued highly by service-users and key stakeholders. Conclusions: The scheme effectively identified, assessed and linked most MDOs to existing services. However, significant changes in mainstream mental health services are required before the full potential of the service can be realized.