Abstract. The study was aimed to find out the prevalence of non-classical congenital adrenal hyperplasia (NC-CAH) due to 21-hydroxylase deficiency (21-OHdef) among Greek women with hirsutism and polycystic ovary syndrome (PCOS) and to compare the results of ACTH stimulated 17-hydroxyprogesterone 60 min (17-OHP60) values, with human leukocyte antigens (HLA) phenotypes, in any patient diagnosed as having NC-CAH. One hundred and seven women with hirsutism and PCOS were included in the study. All were presented at the Reproductive Endocrinology Outpatient Clinic with hirsutism and PCOS. After ACTH stimulation test, 10 women were diagnosed as having NC-CAH because of high 17-OHP60 values ≥36 nmol/l, and 97 as having PCOS. Ten (10.3%) of the 97 women presented hormonal findings compatible with adrenal hyper-response due to ACTH testing, because of hyperstimulated 17-OHP60 values ≥21 nmol/l and <32 nmol/l. The HLA typing of 10 patients with NC-CAH revealed the phenotypes B14, DR1, B35, B7 and B44 which present positively genetic linkage disequilibrium with 21-OHdef, as reported in the literature. In conclusion: In Greek women with hirsutism and PCOS we have found that: a. The prevalence of NC-CAH among these women is relatively high and reaches at 10%. b. The HLA phenotypes B 14, DR 1 , B 35 , B 7 and B44 were found in high frequency in these NC-CAH patients. c. Adrenal NC-CAH due to 21-OHdef as well as adrenal hyperactivity, revealed after ACTH testing, constitutes an important reason of hirsutism and PCOS in these Greek women and both reach a rate of 20%.