A two-stage epidemiologic survey was carried out on a probability sample of the population aged 4 through 16 years in Puerto Rico. The survey used the Child Behavior Checklist as a screening instrument, and prevalence rates were estimated on the basis of clinical diagnoses and other measures provided by child psychiatrists during the second stage. Maladjustment was operationally defined through the use of combined measures, including DSM-III diagnosis and a scale of functional impairment. Data were provided on the demographic correlates of maladjustment and on the comorbidity of DSM-III diagnostic domains. The prevalence rates obtained vis-à-vis the availability of mental health services on the island reflected a major public health problem.