Background: Polycystic ovary syndrome (PCOS) is one of the most common endocrinopathies affecting 5-10% of women of reproductive age. The syndrome is surrounded by controversies regarding both its diagnosis and treatment. The introduction of long-acting GnRH agonists in the late 1980s revolutionized the approach to ovarian stimulation in assisted reproductive technologies by providing the means to downregulate endogenous pituitary gonadotropin secretion and thereby prevent a premature luteinizing hormone surge during exogenous gonadotropin stimulation. The relatively recent introduction of GnRH antagonists in clinical practice has provided another option for ovarian stimulation in IVF. The purpose of this study was to compare the efficacy of the fixed GnRH antagonist vs. GnRH agonist long protocol in patients with polycystic ovary syndrome treated by ICSI. Results: There is a statistically significant difference between both groups in view of the received dose of gonadotrophin (1901.7 ± 400.6 vs. 1789 ± 368 with p = .004) and duration of stimulation (11.3 ± 0.8 vs. 10.3 ± 1.1 with p = .017). There is no significant difference between both groups in view of pregnancy outcome (37% vs. 32% with p = .125). There is a significant difference between both groups in view of ovarian hyperstimulation syndrome (OHSS) incidence where the rates were 15%, 6%, and 1.5% vs. 4.5%, 2.5%, and .05% with p = 0.04 for mild, moderate, and severe, respectively, form of OHSS in group 1 and group 2. Conclusion: The antagonist protocol may be the preferred stimulation protocol for PCOS patients treated by ICSI in view of the reduction of OHSS incidence rates without compromising the pregnancy outcome.