Data were obtained on all the patients under 18 years old who entered a special hospital for the first time between January 1, 1983, and December 31, 1999. Of these, only the patients with a Mental Health Act (1983) classification of mental illness and/or psychopathic disorder were included in the study (n=46). The data covered only the first admission of the patients. A comparison group of adults was matched with the study group on sex, legal classification of detention, and disorder under the Mental Health Act classification. The children were admitted to a special hospital for a range of offenses similar to those of the comparison group; however, the children had been convicted for criminal damage and violence at a significantly earlier age, and they were more likely than the comparison group to have experienced a change in caregiver during their childhood and to have been placed in a children's home. They were also less likely to have been living with a family member on their 16th birthday. Overall, children admitted to a special hospital had a significant degree of disruption in their childhoods compared to the comparison group, and they were involved in a significant amount of multiagency services in the course of their childhood development. In order to serve these adolescents who require high-security care, a separate service for adolescents within a special hospital might be established, or an adolescent medium-security unit could have a subunit that specializes in adolescents who require high-security care. 3 tables, 3 notes, and 40 references