Before total deinstitutionalization in Norway, many believed that the ordinary health care system could give people with intellectual disability the same or even better health care than that which they received in institutions. It was said that institutions created psychiatric problems, and that these would diminish or even disappear with the closing of these establishments. The present study is a prospective cohort study without a control group. It examines the frequency of mental health problems and the psychiatric health services which 109 subjects aged between 16 and 65 years received before (1987) and after (1995) deinstitutionalization. Mental health problems were defined as behavioural disturbances, and psychiatric disorders and symptoms. Psychiatric disorders were identified with the Psychopathology Instruments for Mentally Retarded Adults (PIMRA), which were filled in by the carers. Behaviour disturbances were identified as having occurred or not during the previous year. Psychiatric problems remained frequent, and there was a significant increase in behavioural problems in spite of total deinstitutionalization and improved physical living conditions. Access to qualified help, such as psychologists and psychiatrists, had been substantially reduced. Most mental health problems among people with intellectual disability are not solved by reorganization or deinstitutionalization, and such measures are no substitution for professional assistance.