The study's findings suggest that genetic factors explain a moderate proportion of the variance in low self-control and substance use in both adolescence and adulthood. In addition, bivariate genetic analyses show that the correlation between low self-control and substance use is mostly due to common genetic and non-shared environmental factors. Variation at the level of the genome may impact the etiology of self-control both directly and indirectly through gene-environment correlations. This means that the link between parenting measures and a child's self-control is confounded by their common genes. In addition evocative gene-environment correlations suggest that in effective parenting practices can develop as a result of genetically based behavioral traits of the child. In addition, of the two types of environmental factors, the effects of the non-shared environment tended to explain a significant portion of the variance in self-control. Differential parenting experiences within the home, differential perceived parenting by the child, and/or differential reactions to shared parenting experiences may all impact child development. The study used a subsample of twin pairs from the National Longitudinal Study of Adolescent Health. The final analytical sample consisted of 1,480 individual twins. The measure of low self-control was created by scoring 20 items so that higher values reflected lower levels of self-control. 7 tables and 111 references