Objective: To determine whether the high rate of chromosomal abnormalities in the embryos of an infertile couple were caused by a paternal factor that may have involved the sperm centriole. Design: Case report. Setting: Private IVF program. Patient(s): An infertile couple who underwent IVF-ET because of severe male factor infertility and endometriosis. Intervention(s): Preimplantation genetic diagnosis of chromosomal abnormalities in embryos derived from two cycles of ICSI in which the husband's sperm was used and one in which donor sperm was used. Main Outcome Measure(s): Preimplantation genetic diagnosis with fluorescence in situ hybridization using probes for chromosomes X, Y, 13, 16, 18, and 21, and determination of hCG levels. Result(s): Most of the embryos derived from the cycles in which the husband's sperm was used were chromosomally abnormal (82%), whereas all the embryos derived from the cycle in which donor sperm was used were chromosomally normal. The cycle in which donor sperm was used resulted in an ongoing pregnancy. Conclusion(s): Paternal factors, which most likely derive from the centrosome, can contribute to numerical chromosomal abnormalities, which in turn may predispose to implantation failure. (Fertil Steril(R) 1999;72: 1113-5. (C) 1999 by American Society for Reproductive Medicine).