The objective of the study was to investigate the medical and psychiatric characteristics and needs of detainees held under s.53(2) of the Children and Young Persons Act 1933. A case-note study of all subjects detained under s.53(2) at a young offenders' institution was carried out and their psychologists and medical officer interviewed. The subjects had a high risk of having experienced family disruption, of psychoactive substance abuse, and poor educational progress, and they were more likely than the general population to be Afro-Caribbean or of mixed race. They were psychologically vulnerable and could become suicidal when exposed to risk factors such as bullying and not being visited often by friends and relatives. However, there was a lack of information available about the subjects in many important areas including assessment of needs for special education, of truancy, expulsions, child guidance clinic attendance, and placement on child protection registers. It was not clear whether these young people had been significantly in contact with services as children or whether they had slipped through the net. In conclusion, the most important finding was a worrying lack of information about this group. From the information available they were clearly atypical. More research is needed; more adequate information, for example with respect to physical and sexual abuse, child rearing, education, peer relationships, and contact with specialist health and social services, would assist in the development of services for the treatment of these serious young offenders and for prevention.