Objective: To explore the genetic and environmental influences on DSM-IV conduct disorder (CD) aggressive and nonaggressive subscales, taking into account age and sex differences. Method: A community sample of 1,100 twin pairs (ages 11-18) was interviewed using the Diagnostic Interview Schedule for Children. Bivariate analyses, using variable threshold models accounting for age and sex differences, were used to determine the extent to which the genetic and environmental influences on aggressive and nonaggressive CD domains are shared or unique. Results: The phenotypic correlation between aggressive and nonaggressive CD domains was 0.32. The most parsimonious bivariate model included additive genetic effects and nonshared environmental effects only (AE model). Conclusions: The results of behavior genetic model fitting suggest that the DSM-IV CD domains are influenced by unique genetic and environmental factors, but also share some common genetic and environmental influences. A large percentage of the covariation (61%) is caused by genetic factors. These results are consistent with a previous report on the bivariate heritability of aggressive and nonaggressive antisocial behavior, but extend the findings to DSM-IV domains. (Contains 1 figure and 2 tables.)