OBJECTIVE The clinical symptoms of nonclassic adrenal hyperplasia (NCAH) are identical with polycystic ovary syndrome (PCOS). The aim of our study was to determine the prevalence of nonclassic adrenal hyperplasia (21-hydroxylase-deficiency) in hyperandrogenic women, its biochemical, endocrine and clinical characteristics and to compare them with parameters of patients with ovarian hyperandrogenism. METHODS Since 1999, 298 patients with elevation of at least one androgen and manifestation of one of the clinical androgenic symptoms (oligo/amenorrhea, hirsutism or acne) have been identified in our database. A diagnosis of NCAH was considered when the basal or stimulated 17-hydroxyprogesterone was elevated. RESULTS Only eight patients were identified as having 21- hydroxylase deficient NCAH in the whole group of 298 hyperandrogenic women. Hirsutism and acne were found only in three, two patients, five of them had oligo/amenorrhea. Seven patients had both elevated basal and stimulated 17-hydroxyprogesterone, while in one case only elevation of stimulated level was found. All of the NCAH patients had elevated concentrations of testosterone, six DHEA, lower SHBG was found in four patients. Surprisingly, none of the NCAH patients had increased DHEAS. CONCLUSIONS In our study, the prevalence of NCAH in hyperandrogenic women was 2.68%. Their leading symptom was oligomenorrhea, skin androgenic disorders were a minor clinical problem. None of the NCAH patients had an elevated DHEAS, the androgen dominantly produced by the adrenal glands.