More juveniles are involved in the criminal justice system than ever before. Recent literature reviews speculate that many juvenile detainees have alcohol, drug or mental (ADM) disorders and require services. Yet, no study has ever examined ADM service needs and service utilization among juvenile detainees. Prior studies have focused only on the presence of disorder, and have not examined other aspects of need such as functional impairment. Even these studies, however, have serious methodological problems: (1) Non-Representative Samples; (2) Problems in Measurement; (3) Insufficient Sample Size; and (4) Lack of Comorbidity Data. The proposed project is the first step in the complex task of assessing the extent of impairment and ADM service needs of juvenile detainees. We have two specific aims: (1) ADM SERVICE NEEDS. To assess the ADM service needs (including diagnosis, ADM comorbidity and functional impairment) using a stratified random sample of 1800 male and female juvenile detainees. (2) DETECTION AND SERVICE UTILIZATION. To determine the extent that juvenile detainees who need ADM services receive them, either while in the custody of the criminal justice system or as part of their case disposition. The proposed study has four methodological advantages over prior research: (1) a systematic random sampling strategy; (2) a sufficiently large N (600 females and 1200 males); (3) reliable instruments (e.g., the NIMH Diagnostic Interview Schedule for Children (DISC)); and (4) comorbidity data. The proposed study responds to the NIMH National Plan for Research on Child and Adolescent Mental Disorder, which called for research on mental health services in the juvenile justice system.