ABSTRACTIt is now well known that a higher proportion of people with mental retardation show behavioural and psychiatric disorders compared to their non‐mentally retarded counterparts. However, the exact relationship between psychiatric illness and behavioural disorder in this population is far from clear. There are problems of using the standard diagnostic and classification categories in this population, particularly in those who are severely and profoundly mentally retarded. Recently, there have been many novel approaches to this diagnostic dilemma, including ‘developmental approach’ and ‘psychodynamic approach’. In the Netherlands, the so‐called ‘developmentaldynamic’ approach has been used in the diagnosis and treatment of behavioural and psychiatric disorders in the mentally retarded. There have also been many treatment approaches, including drug therapy, behavioural treatment, psychotherapy, cognitive and social learning. Also the Dutch, Swiss and German traditions have extensive experience in the directive pedagogical treatment of the me