ADHD is a familial disorder with high rates of comorbidity with conduct disorder in childhood and antisocial personality and substance use disorders in adulthood. A growing literature suggests that ADHD with antisocial comorbidity may be nosologically distinct from other forms of ADHD. Previously, we proposed a family-based stratification that defined Antisocial families as those with either conduct disorder or antisocial personality disorder in the probands or relatives. To provide predictive validity for that stratification, we assessed psychopathology in these families 4 years after their initial assessment. Results show that the probands and siblings from Antisocial families had higher rates of psychopathology during the 4-year follow-up period compared with siblings from Non-antisocial and control families. They also had more deviant ratings on the Child Behavior Checklist (especially for anxious/depressed, delinquent, and aggressive behavior). We found fewer group differences in the academic, psychosocial, and intellectual correlates of ADHD. These results confirm and extend previous work indicating that Antisocial ADHD may be a nosologically and clinically meaningful subform of ADHD.