Objective: To improve the efficacy of an IVF-ET program for unstimulated patients with polycystic ovary syndrome (PCOS) with the se of culture for oocyte maturation. Design: Prospective studies with the comparison of different ET procedures from March 1995 through February 1998. Setting: University-affiliate hospital. Patient(s): Ninety-four cycles in 64 consenting patients with PCOS. Intervention(s): Immature oocytes were retrieved from unstimulated patients with PCOS and subsequently cultured and fertilized in vitro. Zygote intrafallopian transfer (ZIFT), uterine ET, or a combined approach of ZIFT + uterine ET was subsequently performed. Main Outcome Measure(s): Laboratory and clinical data. Result(s): Among 1,280 immature oocytes (13.6 +/- 7.5 oocytes per patient) retrieved, 89% (1,139) were morphologically normal, and 62.2% (708/1,139) of the normal oocytes matured in vitro after culture for 48 hours. When intracytoplasmic sperm injection was performed, 68% (481/708) developed to the normal pronuclear stage, and 88.1% of the embryos cocultured with Vero cells (266/302) cleaved. Eighty-five ET cycles were conducted and pregnancy was established in 23 cycles (27.1%), which consisted of 8 after uterine ET and 15 after a combined approach. Seventeen patients delivered 20 normal infants. Conclusion(s): The IVF-ET method using no ovarian stimulation followed by in vitro maturation culture can be a feasible assisted reproductive technology for treatment of PCOS with various complications. (Fertil Steril(R) 2000;73:978-83. (C) 2000 by American Society for Reproductive Medicine).