Developmental studies of antisocial behavior (ASB) have found two subgroups of behaviors, roughly described as aggressive and nonaggressive ASB. Theoretical accounts predict that aggressive ASB, which shows greater stability, should have high heritability. In contrast, nonaggressive ASB is very common in adolescence, shows less continuity, and should be influenced both by genes and shared environment. This study explored the genetic and environmental influences on aggressive and nonaggressive ASB in over 1,000 twin pairs aged 8–9 years and again at 13–14 years. Threshold models were fit to the data to incorporate the skew. In childhood, aggressive ASB was highly heritable and showed little influence of shared environment, whereas nonaggressive ASB was significantly influenced both by genes and shared environment. In adolescence, both variables were influenced both by genes and shared environment. The continuity in aggressive antisocial behavior symptoms from childhood to adolescence was largely mediated by genetic influences, whereas continuity in nonaggressive antisocial behavior was mediated both by the shared environment and genetic influences. These data are in agreement with the hypothesis that aggressive ASB is a stable heritable trait as compared to nonaggressive behavior, which is more strongly influenced by the environment and shows less genetic stability over time.