The paper measures delinquency in a number of ways to account for important theoretical distinctions in the delinquency literature. It uses kinship structure in the National Longitudinal Survey of Youth (NLSY) to estimate genetic and shared environmental influences on self-reported delinquency scores. The paper's analytic model is based on DF analysis, a regression procedure used to estimate parameters reflecting genetic and environmental influence. Results suggest a consistent and moderate genetic basis to sibling similarity in delinquency and little evidence of a shared environmental basis. A large amount of variance is attributable to nonshared influences and/or measurement error. Findings suggest that the search for environmental influences on adolescent delinquency should focus on those that are not shared by siblings. The paper considers that the approach used for this study is methodologically valuable, since it allows for the simultaneous estimation of a number of sources of influence, as reflected in the similarities and differences among related kin from multiple levels of kinship. Tables, references