OBJECTIVE To determine the factors that influence the number and quality of embryos produced from primary oocytes collected from untreated regularly ovulating and irregular or anovulatory polycystic women. METHODS A direct comparison between two patient groups whose oocytes were matured in vitro and a comparison of the embryo development of in vitro-matured oocytes from untreated patients with in vivo-matured oocytes of superovulated IVF-ET patients obtained during the same period. METHODS The Monash IVF Clinic, involving patients who expressed the desire to avoid super-ovulation with fertility drugs. METHODS The completion of nuclear maturation of oocytes after 36 or 48 hours culture, fertilization in vitro, and embryo development ratio. RESULTS Oocytes from regular cycling patients matured and fertilized at significantly higher rates than irregular cycling and anovulatory women and their embryos had significantly higher mean embryo development ratio. The mean embryo development ratio of embryos of regular cycling patients was similar to superovulated IVF patients but irregular cycling and anovulatory patients had a significantly lower embryo development ratio. Culture of oocytes for 48 hours increased maturation of oocytes from 57% to 82% but did not affect fertilization or cleavage rates. Embryo development was not affected significantly by the grade of follicular cell cover of oocytes. CONCLUSIONS The developmental capability of primary oocytes is higher in regular cycling women than in irregular cycling and anovulatory women with polycystic ovary disease.