Objective: The aim of the study was to examine the relationship of prevalence and age at onset of drug abuse and dependence to mood and anxiety disorders, using epidemiologic data. Methods: Lfe-table analyses using data collected on 20,745 respondents in the National institute of Mental Health's Epidemiologic Catchment Area surveyswere used to calculate the hazard rate for developing drug disorders subsequent to adolescent onset or adult-onset mood and anxiety disorders. Results: For respondents with onset of a mood disorder during adolescence, the peak age for developing drug abuse and dependence occurs between 15 and 19 years; when the mood disorder begins in adulthood, the peak onset for drug disorders is delayed to between 25 and 29 years of age. Similar but less striking results are found for onset of drug abuse and dependence following either panic or obsessive-compulsive disorder. Conclusions: These findings highlight the need for future prospective studies of children and adolescents to date the onset of mental disorders and substance use disorders. if prospective studies can confirm the apparent pattern of substance use disorders occurring subsequent to mental disorders, prevention and treatment strategies for youth at risk should be developed.