This study examined possible gender differences in children and adults with attention-deficit/hyperactivity disorder. Results indicated that adult self-ratings differed significantly by gender. Adult women reported fewer assets and more problems than did male counterparts, but there was no gender difference with respect to age at referral, intelligence quotient, indicators of neuropsychological performance, or parent or teacher ratings of behavior. Referral bias against girls is a possible reason for previously reported gender differences, so we interpreted our results in light of the participants' referral patterns. There was a nonsignificant trend for girls with relatively more severe ratings of hyperactivity, conduct disorder, or inattention to be referred earlier than were boys. Overall, our results suggest no evidence of cognitive or neuropsychological differences by gender in samples that are sensitive to behavioral deviance in girls (as evidenced by early referral), but adult women's self-perception is comparatively poorer than that of adult men.