Impulsivity and inattention are key constructs at the interface of temperament and domains of childhood behavioral problems, such as ADHD and ODD. A multi-method, multi-source assessment of impulsivity and inattention was conducted with 256 families of twins at a mean age of 8-9 years from an epidemiologically defined community sample. Analysis of 20 impulsivity, inattention, and related behavior-problem measures yielded a single principal component, which could also be decomposed into five narrower factors. These narrower factors distinguished inattention and impulsivity content from more defiant content, and split the domain by method of assessment. Males scored significantly higher on factors related directly to impulsivity and inattention. Lower socioeconomic status also predicted impulsivity and inattention, as well as defiance and aggression, and lower IQ modestly predicted impulsivity and inattention. Biometric analyses showed that these multi-source measures of childhood impulsivity and inattention were highly heritable, with genetic variance accounting for 70-80% of the phenotypic variance in many of the models. Shared environmental factors were generally not influential, and nonshared environmental effects were stronger for males than for females for inattention/impulsivity. These results suggest that impulsivity and inattention during this period of childhood are (1) clearly related to concurrent aggressive/defiant symptoms; (2) multidimensional, with influences of method of assessment on outcome; and (3) highly heritable, with possible gender differences in the strength of genetic effects.