This study examined the construct validity of antisocial personality disorder (ASPD) diagnosed in adolescence. Boys and girls were grouped by history of DSM-III-R conduct disorder (CD) and ASPD: Controls (n = 340) had neither diagnosis; CD Only (n = 77) had CD by age 17 but no ASPD through age 20; Adolescent ASPD (n = 64) had ASPD by age 17. The Adolescent ASPD group was then compared to 20 young adult men who met criteria for ASPD (ASPD group). As expected, the Adolescent ASPD group had significantly more depression and substance use disorders, a greater performance greater than verbal IQ discrepancy, more deviant peers, and poorer academic functioning than the CD Only group and Controls. The Adolescent ASPD and ASPD groups did not differ on most variables. Results support the construct validity of Adolescent ASPD and suggest that such a diagnosis could help identify adolescents at risk for persistent antisocial behavior.