Six geographically representative areas across England and Wales were selected for the study, with each containing a youth offending team (YOT) and secure juvenile facility. A total of 151 juvenile inmates and 150 juveniles under community supervision were interviewed, using assessment instruments to obtain data on demographics, mental health, and social needs. Eighty semistructured interviews were conducted with key stakeholders to determine the structures and processes for services and the observed outcomes. In order to identify what works with juvenile offenders in addressing mental health needs and offending behavior, a literature review was conducted. One-third of juvenile offenders were found to have a mental health need, with those in the community having significantly more needs than those in secure care; however, there was no routine mental health assessment on admission to secure sites and a lack of appropriate mental health intervention programs in secure facilities. Mental health services for juvenile offenders supervised in the community were not uniformly available, with inadequate funding and resources being major problems. Continuity of care was a frequent problem. There should be structured assessments for risk and mental health needs for all youth entering secure and community-based corrections as the basis for planned interventions tailored to the needs of each youth. The most effective interventions have used cognitive behavioral therapy and training in problem-solving skills; and all interventions should be delivered by well-trained staff. Interventions should be evaluated for their effectiveness. 9 tables, 6 figures, 52 references, and appended study instruments