BACKGROUND: We undertook this study to determine whether the widely replicated link between maternal smoking and conduct disturbance (Cd) is better explained by a model of direct causation or of mother-offspring transmission of a latent Cd variable. METHODS: Family data collected on 538 adolescent twin boys from the Virginia Twin Study of Adolescent Behavioral Development (VTSABD) was used to compare two alternative models: 1) a model composed of a latent transmissible factor that influences mother's juvenile conduct symptoms, smoking during pregnancy, and subsequent Cd and smoking in her adolescent boys; and 2) a model specifying a direct causal path from mother's smoking to child Cd. RESULTS: The maternal-offspring transmission model fit the data as well as a model specifying a direct causal path from maternal smoking to child Cd. CONCLUSIONS: Our results suggest that the association between maternal smoking during pregnancy and boys' Cd symptoms may be attributed to the transmission of a latent Cd factor and not to a direct effect of the smoking. Our results challenge previous findings of a direct effect of prenatal smoke exposure on risk to Cd once other etiologic factors are considered.