IMPORTANCE: Psychiatric disorders and comorbidity are prevalent among incarcerated juveniles. To date, no large-scale study has examined the comorbidity and continuity of psychiatric disorders after youth leave detention. OBJECTIVE: To determine the comorbidity and continuity of psychiatric disorders among youth 5 years after detention. DESIGN, SETTING, AND PARTICIPANTS: Prospective longitudinal study of a stratified random sample of 1829 youth (1172 male and 657 female; 1005 African American, 296 non-Hispanic white, 524 Hispanic, and 4 other race/ethnicity) recruited from the Cook County Juvenile Temporary Detention Center, Chicago, Illinois, between November 20, 1995, and June 14, 1998, and who received their time 2 follow-up interview between May 22, 2000, and April 3, 2004. MAIN OUTCOMES AND MEASURES: At baseline, the Diagnostic Interview Schedule for Children Version 2.3. At follow-ups, the Diagnostic Interview Schedule for Children Version IV (child and young adult versions) and the Diagnostic Interview Schedule Version IV (substance use disorders and antisocial personality disorder). RESULTS: Five years after detention, when participants were 14 to 24 years old, almost 27% of males and 14% of females had comorbid psychiatric disorders. Although females had significantly higher rates of comorbidity when in detention (odds ratio, 1.3; 95% CI, 1.0-1.7), males had significantly higher rates than females at follow-up (odds ratio, 2.3; 95% CI, 1.6-3.3). Substance use plus behavioral disorders was the most common comorbid profile among males, affecting 1 in 6. Participants with more disorders at baseline were more likely to have a disorder approximately 5 years after detention, even after adjusting for demographic characteristics. We found substantial continuity of disorder. However, some baseline disorders predicted alcohol and drug use disorders at follow-up. CONCLUSIONS AND RELEVANCE: Although prevalence rates of comorbidity decreased in youth after detention, rates remained substantial and were higher than rates in the most comparable studies of the general population. Youth with multiple disorders at baseline are at highest risk for disorder 5 years later. Because many psychiatric disorders first appear in childhood and adolescence, primary and secondary prevention of psychiatric disorders offers the greatest opportunity to reduce costs to individuals, families, and society. Only a concerted effort to address the many needs of delinquent youth will help them thrive in adulthood.