The paper describes a special hospital-based treatment programme for male mentally handicapped offenders, comprising a package of practical and personal skills training coupled with a socialisation programme based on token-economy strategies within a controlled and structured environment. Twenty patients admitted to the programme and followed up after discharge for an average of 3.3 years were studied in detail. All had committed serious or persistent offences and showed a high level of psychosocial pathology. A good or fair response to the treatment programme was made by 85%, and 65% were judged well adjusted or reasonably well adjusted at last follow-up contact. A good outcome was associated with more than two years' in-patient care, a good response to the treatment programme and stable residential placement, regular occupation and regular supervision and support in the community. Offenders against the person (sex and assault) had a better prognosis than and showed other interesting differences from property offenders (property and arson).