We examined the genetics of impulsive traits in children and adolescents in the Barratt Impulsivity Scale (BIS) in a longitudinal twin study between the ages of 9- and 16-years old. Comparisons of monozygotic (MZ) and dizygotic (DZ) twin correlations suggest a significant heritability to each of the three impulsivity subscales in the BIS, including non-planning, motor impulsivity, and inattention. While a single common factor model fit the data well on two different occasions, some scale specific genetic variance also exists, particularly for inattention and non-planning, suggesting the multifactorial nature of impulsivity. The genetic influence on the common factor of impulsivity was somewhat larger in early adolescence (h2=0.57) than in mid-adolescence (h2=0.42). The relationship of the BIS impulsivity scales to laboratory measures of impulsivity (i.e., errors of commission and reaction times in the NoGo task and risky decision making in the Iowa Gambling Task) will also be investigated, in an effort to understand further the multi-factorial nature of impulsivity and its etiology in children and adolescence. Results from this study can be used to better our understanding of a construct underlying several psychiatric disorders and categories of antisocial or risky behavior.