Objective: To determine whether the incidence of apoptosis in mature oocyte cumulus cells changes after insemination related to infertility. Design: Prospective study. Setting: Public hospital and university. Patient(s): One hundred women undergoing in vitro fertilization and embryo transfer (IVF-ET). Intervention(s): Collection of cumulus cells from IVF-ET cycles with different infertility etiologies. Main Outcome Measure(s): Detection of apoptosis in cumulus cells; fertilization, embryo quality, and pregnancy rate. Result(s): The incubation of cumulus-oocyte-complexes with spermatozoa led to an increase in cumulus cell apoptosis from 34.2 ± 3.7 to 44.5 ± 6.3%. After insemination, cumulus cells of poor quality embryos showed a statistically higher apoptotic rate versus cumulus cells of good quality embryos (61.5 ± 6.4 vs. 40.6 ± 3.9%). Cumulus cells arising from oocytes with ≥50% fertilization rates after insemination showed higher apoptosis rates did cumulus cells from oocytes with <