Inactivating mutations in the enzyme hexose-6-phosphate dehydrogenase (H6PDH), the enzyme responsible for NADPH generation playing critical role in 11-hydroxysteroid dehydrogenase type 1 (11b-HSD1) activity, cause apparent cortisone reductase deficiency (ACRD). It leads to increased metabolic clearance rate of cortisol due to a defect in cortisone to cortisol conversion by 11b-HSD1. We want to analyse the process of the disease, efficacy of long-lasting treatment with glucocorticoids throughout childhood and adolescence in only male patient with ACRD.A 23 year-old male patient was diagnosed with ACRD at the age of 7 years. The clinical manifestation of ACRD was presented by precocious pubarche. His bone age was assessed as 11.5 years old. Blood tests indicated increased the plasma androgen, with elevated 17-hydroxyprogesterone concentration. A steroid profile analysis of a 24-h urine collection showed extremely reduced THF + allo-THF/THE ratio - 0.021 (normal range: 0.7-1.2). Two months of hydrocortisone therapy was ineffective and dexamethasone was administered in initial dose of 0.375 mg/24 h. Next dosage beetwen 0.125 mg/24h and 0.375 mg/24h has been changed depending on the patient's results of laboratory tests and condition. Control laboratory studies indicated suppression of excess adrenal androgen synthesis, but we never got the THF + allo-THF/THE ratio in normal values. He did not develop any serious side effects, although dexamethasone is the most potent adrenal suppression drug.Hydrocortisone treatment is ineffective in ACRD patients because it was rapidly metabolized to cortisone. We have found the balance between the dexamethasone treatment effects of adrenal suppression and the achievement of full height potential considering the condition of our patient.