Children with congenital adrenal hyperplasia (CAH) and adrenal insufficiency (AI) require daily hydrocortisone replacement with accurate dosing.Prospective study of efficacy and safety of hydrocortisone granules in children with AI and CAH monitored by 17-OHP saliva profiles.17 children with CAH (9 male) and 1 with hypopituitarism (male) aged from birth to 6 years, had their hydrocortisone medication changed from pharmacy compounded capsules to hydrocortisone granules. Patients were followed prospectively for 2 years. In children with CAH therapy was adjusted by 3-monthly 17-OHP profiles. The following parameters were recorded: hydrocortisone dose, height, weight, pubertal status, adverse events, and incidence of adrenal crisis.Study medication was given thrice daily, median duration of treatment (range) was 795 (1-872) days with 150 follow-up visits. Hydrocortisone doses were changed on 40/150 visits, 32 based on salivary measurements and 8 on serum 17-OHP levels. Median daily hydrocortisone dose mg/m 2 (range) at study entry in different age groups: 2-8 years, 1months-2years, <28 days was 11.9 (7.2-15.5), 9.9 (8.6-12.2) and 12.0 (11.1-29.5) and at end of study was 10.2 (7.0-14.4), 9.8 (8.9-13.1) and 8.6 (8.2-13.7). There were no trends for accelerated or reduced growth. No adrenal crises were observed despite 193 treatment-emergent adverse events, which were mainly common childhood illnesses.This first prospective study of glucocorticoid treatment in children with AI and CAH demonstrates that accurate dosing and monitoring from birth results in hydrocortisone doses at the lower end of the recommended dose range, normal growth, without occurrence of adrenal crises.