Abstract Purpose Patients with classic congenital adrenal hyperplasia (CAH) are treated postnatally with life-long glucocorticoid (GC) replacement therapy. Although prolonged exposure to GCs may have a negative impact on behaviour, few studies have studied this issue. We therefore investigated behavioural outcomes in male and female children and adolescents with CAH. Methods An observational study in which Swedish and Italian children and adolescents with CAH identified through neonatal screening for CAH (n = 57, age range 7–17 years) were compared with healthy population controls matched for age and sex (n = 72, age range 7–17 years). Thirteen (eight females) of the fifty-seven children and adolescents with CAH had been treated prenatally with dexamethasone (DEX). Standardised questionnaires for parents and self-report scales for children/adolescents were used to assess behavioural and emotional problems, social anxiety, temperament and scholastic competence. Results There were no statistically significant differences between CAH patients (not prenatally treated with DEX) and controls on most of the scales measuring adaptive functioning or behavioural problems. However, children with CAH were rated by their parents to have more social problems than controls (Child Behaviour Checklist, CBCL social problems, p = 0.032). In the small group (n = 13) of prenatally DEX-treated cases parents rated their children/adolescents to have more mood problems compared with non-DEX-treated children/adolescents with CAH (CBCL-withdrawn/depressed, p = 0.019). Conclusion Children/adolescents with CAH showed good overall adjustment. The clinical significance of the parentally perceived increase in social problems in children/adolescents with CAH requires further investigation. The findings underline the importance of psychological support for children/adolescents with a chronic condition.