Abstract Context Patients with classic congenital adrenal hyperplasia (CAH) are treated postnatally with lifelong glucocorticoid (GC) replacement therapy. Previous results on general cognitive ability in individuals with CAH have been conflicting. Objective To evaluate long-term cognitive effects of GC replacement therapy and the impact of early diagnosis in children with CAH. Design and Setting Observational study with patients from a single research institute. Patients 32 children with CAH (mean age 11.5 years) identified through the Swedish national neonatal screening program for CAH and 52 matched population controls (mean age 10.7 years). Eleven (6 female) children with CAH who were treated prenatally with dexamethasone (DEX), (CAH-DEX) (mean age 11.7 years). Intervention GC replacement therapy, neonatal screening for CAH. Measures Cognitive abilities assessed with standardized neuropsychological tests (Wechsler scales, Span Board Test, Stroop Interference Test, NEPSY list learning). Results Children with CAH (not prenatally treated) performed equally well as population controls on a series of tests assessing general intellectual ability and executive functions. No significant differences were observed in cognitive performance between patients with different genotypes (null, non-null). Patients with salt-wasting CAH performed poorer than patients with simple virilizing CAH in a test assessing visuo-spatial working memory (P = 0.039), although the performance was within the normal range for the population. Prenatally DEX-treated girls with CAH had lower verbal intellectual ability compared with CAH girls not exposed to prenatal treatment (P = 0.037). Conclusion Children and adolescents with CAH who were diagnosed early via a neonatal screening program and treated with hydrocortisone had normal psychometric intelligence and executive functions.