Girls with congenital adrenal hyperplasia (CAH) exhibit behavioral masculinization. There is controversy about the roles of pre-and postnatal androgens, social factors, and chronic illness in its etiology.To assess the effect of chronic illness, we compared behavioral masculinity in 24 CAH girls and 25 diabetic girls aged 3-12 yr from Manchester using two sensitive questionnaires, and an overall masculinity score M (high ؍ masculine) was derived.To assess the contributions of pre-and postnatal androgens, the CAH subjects were categorized into genotype groups (G) according to the reported severity of loss of CYP21 function: G1 (n ؍ 10, null mutations), G2 (n ؍ 9, intron 2G), G3 (n ؍ 3, I172N), and G4 (n ؍ 2, unknown loss of function). In CAH girls, relationships between G, Prader degree of genital masculinization at birth, bone age advance, and M were assessed.CAH girls were less feminine and more masculine than diabetic girls (P < 0.001), who were not significantly different from U.S. controls. Among the CAH girls, those in G1 and 2 were more genitally masculinized than those in G3 and 4 (P < 0.009) and had higher M (P < 0.025). M was negatively correlated with advanced bone age (r ؍ ؊0.5; P ؍ 0.02).CAH