This study was designed to evaluate the changes of serum levels of leptin, leutinizing hormone (LII), follicle stimulating hormone (FSH), testosterone and plasma neuropeptide Y (NP)) in polycystic ovary syndrome (PCOS) patients as a trial to find a possible relationship between these parameters. The study comprised 74 females; 38 patients with anovulatory PCOS diagnosed by imaging studies and 36 normally ovulating females (control group). All patients underwent full history taking, determination of weight (if?), height (Ht) and body mass index (BMI). Fasting blood samples was collected from all study participants at 8-9 AM on day 2-4 of menstrual cycle for estimation of plasma NPY level, serum leptin, testosterone, FSH and LH using ELISA technique. There were 23 obese (mean BMI-36±3.6) and 15 lean (mean BMI=23.9f0.6) patients with PCOS. Among the control group there were 18 obese (mean BMI = 31.8±4.8) and 18 lean (mean BM= 22.6±1.71). There were significant increase in serum testosterone, LH and LH/FSH ratio while there was a significant decrease of serum FSH in patients compared to control group. Serum leptin concentration was significantly increased in patients (obese or lean) compared to controls, with a significant increase in obese compared to leans in both groups (PCOS group & control). Plasma NPY concentration showed significant increase in patients; obese and lean, compared to controls with a non-signijicant d ference between obese and leans in both groups. Serum leptin showed a.positive significant correlation with BMI, in both groups and with serum testosterone in PCOS group, but showed a negative significant correlation with plasma NPY in control group while there was a positive but non-significant correlation with plasma NPY in PCOS patient group. Serum leptin showed a positive non-significant correlation with serum LH and FSH in both groups. It could be concluded that there was a state of hyperleptinemia in women with PCOS especially the obese and this hyperleptinemia correlates with BMI & testosterone but it is not affected by the circulating level of FSH, LH and NPY levels. However, the exact roles of hyperleptinemia and increased NPY in pathogenesis of PCOS still need to be clarified.