Context: Congenital adrenal hyperplasia (CAH) is a disorder with a wide spectrum of severity.

Objective: To investigate cognitive function in CAH women.

Design: A case-control study.

Setting: A tertiary center for pediatric endocrinology at the University Hospital of Copenhagen.

Participants: Thirty-five Danish CAH women (age 17-51 yr) were included, participation rate 84%. Control women were recruited through the Danish Civil Registration System and matched on age and education.

Main Outcome Measures: An abbreviated form of the Wechsler Adult Intelligence Scale, i.e. full scale IQ (5 of 11 subtests), which included 3 of 6 verbal IQ subtests and 2 of 5 performance IQ subtests.

Results: A significantly lower IQ was found in CAH patients compared with controls with respect to mean full scale IQ (84.5 vs. 99.1; P < 0.001), mean verbal IQ (86.6 vs. 97.3; P < 0.001), and mean performance IQ (85.7 vs. 101.3; P < 0.001). The salt-wasting CAH group had lower IQ-scores than the simple-virilizing CAH group, which reached significance for mean total IQ (81.2 vs. 92.8, P = 0.04) and mean verbal IQ (84.7 vs. 95.5, P = 0.05), and additionally, lower scores than the late-onset CAH group, which reached significance for performance IQ (mean 81.5 vs. 96.2, P = 0.02).

Conclusions: Impaired cognitive function was observed in patients with CAH, especially in salt-wasting CAH. These intriguing findings may reflect adverse effects of hyponatremic episodes, sub-optimal postnatal hormone replacement therapy or prenatal adrenal androgen excess, as well as the potential psychosocial consequences of the disorder.