Polycystic ovarian syndrome (PCOS) is a prevalent endocrine disorder, which is the most common cause of anovulatory infertility and hirsutism. It is caused by an overproduction of androgens in theca cells. In the ovary, androgen synthesis is regulated by 17 alpha-hydroxylase/17,20-lyase enzyme complex containing P450c17 (CYP17). In some individuals, the promoter region of CYP17 gene contains a T-->C substitution that creates an Sp1 site at position-34. This polymorphism generates a recognition site for the MspA1 restriction enzyme. The objective of the study was to investigate the frequency of T-->C substitution of CYP17 gene promoter in women with PCOS and elucidate its role in the pathogenesis of the syndrome. Another aim of the study was to compare the results with the levels of the hormones luteinizing hormone, follicle-stimulating hormone, testosterone and estradiol. The present investigation involved a group of 55 women with PCOS and 56 healthy women without symptoms of PCOS. Following digestion with restriction enzyme MspA1, it was demonstrated that the polymorphic A2 allele is no more frequent in women with PCOS than in healthy women. In the PCOS group, the hormonal profiles were not significantly different in the carriers of a normal allele A1A1 from the carriers of A1A2 and A2A2 alleles. It is concluded that T-->C polymorphism of CYP17 gene is not associated with steroid hormone synthesis in PCOS and is not the primary genetic defect in this disease.