Objective: To examine the social, family background, and individual antecedents of conduct disorder (CD) and oppositional defiant disorder (ODD), the extent to which CD and ODD symptoms were predicted by common environmental risk factors, and the extent to which the antecedents of CD and ODD accounted for the comorbidity between the two disorders. Method: Data were gathered from 926 members of a New Zealand longitudinal birth cohort. The outcome measures were DSM-IV symptom count measures of CD and ODD at age 14 to 16 years. Predictors measured during the period from 0 to 14 years included the following: maternal smoking during pregnancy; exposure to socioeconomic adversity; parental maladaptive behavior; childhood exposure to abuse and interparental violence; gender; cognitive ability; and affiliation with deviant peers in early adolescence. Associations between the predictors and outcome measures were modeled using structural equation modeling. Results: The analyses showed that each of the predictors was significantly (p less than 0.05) associated with CD and ODD, with the exception of gender and ODD. After model fitting, the profile of risk factors that predicted CD and ODD were largely similar. The analyses revealed that approximately 40% of the comorbidity between disorders could be accounted for by common factors. Conclusions: The data showed that CD and ODD had largely similar social and environmental antecedents. One implication of this finding is that treatment and prevention approaches that are developed for use with a particular behavior disorder may in fact reduce the incidence of both disorders. (Contains 1 figure and 2 tables.)