A retrospective study of all Swedish patients with congenital adrenal hyperplasia (CAH) born 1969-1986, was conducted to elucidate possible benefits of neonatal screening for CAH. Information was obtained about 150 patients (67 male, 83 female). One hundred and forty-three cases were regarded as classical and seven as non-classical (symptoms after 5 years of age or cryptic). All but two (one girl with 11-hydroxylase deficiency and one boy with beta-hydroxysteroid-dehydrogenase deficiency) had 21-hydroxylase deficiency. The prevalence was 1:11,500. Ninety-three patients (48 male, 45 female) displayed salt loss, all before the age of 3 months. Two boys had died and many children had been critically ill during the first weeks of life. The median age at diagnosis for boys in this group was 21 days. Gender assignment was a major problem in 38 of 57 girls with ambiguous genitalia noticed during the first day. Fifteen of these girls were considered to be male for their first 40 days (median), before the CAH diagnosis was established. Patients in whom the first symptom was manifested after the age of one year often showed growth acceleration, which frequently was overlooked. Median diagnostic delay in this group was 17 months. Possible benefits of neonatal screening are: avoidance of a serious salt-loss crisis; earlier diagnosis and correct gender assignment in virilized girls; decreased virilization, growth acceleration and premature pubarche in prepubertal children; and reduced negative consequences for psycho-social development and final height.