Background: Because the epidemiologic data available for adolescents from the developing world is scarce, the objective is to estimate the prevalence and severity of psychiatric disorders among Mexico City adolescents, the socio-demographic correlates associated with these disorders and service utilization patterns. Methods: This is a multistage probability survey of adolescents aged 12 to 17 residing in Mexico City. Participants were administered the computer-assisted adolescent version of the World Mental Health Composite International Diagnostic Interview by trained lay interviewers in their homes. The response rate was 71% (n = 3005). Descriptive and logistic regression analyses were performed considering the multistage and weighted sample design of the survey. Results: One in every eleven adolescents has suffered a serious mental disorder, one in five a disorder of moderate severity and one in ten a mild disorder. The majority did not receive treatment. The anxiety disorders were the most prevalent but least severe disorders. The most severe disorders were more likely to receive treatment. The most consistent socio-demographic correlates of mental illness were sex, dropping out of school, and burden unusual at the adolescent stage, such as having had a child, being married or being employed. Parental education was associated with treatment utilization. Conclusions: These high prevalence estimates coupled with low service utilization rates suggest that a greater priority should be given to adolescent mental health in Mexico and to public health policy that both expands the availability of mental health services directed at the adolescent population and reduces barriers to the utilization of existing services.