Males are more likely than females to show aggressive behavior across species, ages, and situations, and these differences may be partly influenced by early hormones. We studied aggression in three samples of subjects with congenital adrenal hyperplasia (CAH), who were exposed to high levels of androgen in the prenatal and early postnatal periods. Controls were siblings and first cousins similar in age. In Sample 1, adolescents and adults completed the Multidimensional Personality Questionnaire (MPQ), which includes an Aggression scale. In Sample 2, adolescents and adults completed the MPQ and a paper-and-pencil version of Reinisch's Aggression Inventory. In Sample 3, parents rated the aggression of children aged 3-12, using a modification of Reinisch's Inventory. In all three samples, control males had higher aggression scores than control females. Further, as predicted, females with CAH had higher aggression than control females, but the difference was significant only in adolescents and adults. These results suggest that early androgens contribute to variability in human aggression.