Background: Polycystic ovary syndrome(PCOS) is the most common endocrinopathy in women and the most common causes of anovulatory infertility.Inadequate follicule stimulating hormone is hypothesized to be a proximate cause of anovulation.Inhibins are glycoprotein hormone produced by the granulosa and theca cells of the ovary that selectivly inhibits FSH production and or release from the pituitary. The possible role of inhibin in the etiology of polycystic ovary syndrome (PCOS) is controversial. This study was designed to investigate levels of serum inhibin in women with PCOS. Methods: In a case-control setting 41 women with PCOS from the endocrine and gynecology and obstetrics clinic of Shariati Hospital and 44 women with normal cycles (control group) aged 15-40 year-old were evaluated. In all patients with PCOS and control women appropriate medical history was taken and physical examination was done.Serum inhibin levels were compared in two groups. Statistical analysis was performed using the Mann -Whitney U test Results: Mean age of cases and controls was 23.6±5.3 and 23.1 ±3.9 years, respectively. Mean body mass index (BMI) in cases and controls were 25.07±5.45 and 21.33± 2.46 Kg/m2, respectively. There was no statistically significant difference in mean age between the two groups (p > 0.05) but mean BMI was significantly different between the two groups (p < 0.001). Mean serum levels of inhibin in cases and controls were 1.62±1.23 and 2.26±2.26 U/ml, respectively which was not significantly different between the two groups (p: 0.168). Conclusion: There was no significant difference in serum inhibin levels between patients with PCOS and healthy women. We concluded that basal inhibin levels cannot be used for routine screening in women with PCOS. Further study is needed to determine the role of inhibin in these patients with assay of its two subunits (Inhibin A and B).