This bulletin examines the prevalence of alcohol, drug, and mental disorders among youth at the Cook County (Illinois) Juvenile Temporary Detention Center, by gender, race/ethnicity, and age. Drawing on research conducted by the Northwestern Juvenile Project, this bulletin finds that nearly two-thirds of males and three-quarters of females studied met diagnostic criteria for one or more psychiatric disorders. The Bulletin presents information that can help the juvenile justice system detect youth psychiatric disorders and respond with an integrated system of services. (Contains 6 tables and 2 figures.)