Lahey and Waldman (2003, 2005) proposed a model in which three dispositions--sympathetic response to others; negative emotional response to threat, frustration, and loss; and positive response to novelty and risk--transact with the environment to influence risk for conduct disorder (CD). To test this model, the Child and Adolescent Dispositions Scale (CADS) was developed to measure these dispositions using parent ratings of the child. Here we report psychometric evaluations of a parallel youth self-report version (CADS-Y). Exploratory factor analysis of CADS-Y items among 832 9- to 17-year-olds yielded a 3-factor structure that was consistent with the model and invariant across sex and informants. In 1,582 pairs of 9- to 17-year-old twins, confirmatory factor analyses supported the CADS-Y 3-factor model. Each CADS-Y dimension was associated with CD and related personality dimensions as predicted. (Contains 7 tables and 2 figures.)