In this article we analyse the central features of the establishment and development in Norway of a mental health service for children. Influenced by the movements for mental hygiene and child guidance from the 1920s, Norwegian psychiatrists turned their attention increasingly towards prevention of mental and social problems. During the 1930s, IQ-testing and segregation of troublesome children from school became an important tool for handling children with mental or behavioural problems. With increasing public attention, child mental health activities grew from the late 1940s, and the first regular therapeutic clinic for children was established in 1947. Therapeutic ideas derived from psychoanalytical theory and applied in the new clinics, challenged the dominant view of segregation as a solution to mental and social problems. From 1961 a comprehensive mental healthcare service for children was developed in Norway, and the aim of therapeutic treatment changed gradually from segregation to integration.