Introduction: Polycystic ovary 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 androgen in theca interna cells. In the ovary, androgen synthesis is regulated by CYP17 gene, which encodes a single P450c17with both 17α-hydroxylase/17,20-lyase activities. In PCO patients, the promoter region of CYP17 gene contains a T→ C substitution that leads to overexpression of that gene and creates a Sp1 site at position-34. This polymorphism generates a recognition site for the MspA1 restriction enzyme.Subjects and methods: The present study was conducted on 28 PCOS patients compared to a control group of 26 healthy females of matching age. Serum levels of the hormones LH, FSH, free T. and DHEA-S were measured and the frequency of T→ C substitution CYP17 gene promoter was investigated in all patients and controls.Results: The wild A1A1 alleles were found in 7 patients with PCOS (25%) and in 6 healthy women (23.1%). In 18 patients with PCOS (64.3%) and in 15 healthy women (57.7%), heterozygous A1A2 alleles were found. Homozygous A2A2 alleles were found in 3 patients with PCOS (10.7%) and in 5 healthy women (19.2%) There was no significant difference in the frequencies of CYP17 genotypes (A1A1), (A1A2),(A2A2) in PCOS patients compared with those in healthy women. Moreover, hormonal profiles were not significantly different in the patients with PCOS from both the homozygous and the heterozygous groups.Conclusions: T→ C polymorphism CYP17 gene is not the primary genetic defect in PCOS and is not associated with steroid hormone synthesis in this disorder.