One hundred and sixteen couples with severe male factor infertility underwent 139 subzonal sperm microinjection cycles. In total, 1343 oocytes were microinjected, resulting in a fertilization rate of 24%, followed by a cleavage rate of 65%. In 26% of the zygotes, fertilization was delayed and embryos derived from these zygotes demonstrated a poor capacity for further growth and implantation. In 102 of 139 cycles (73%) embryo transfer was performed, resulting in 9 pregnancies. This study followed the fate of injected oocytes and early embryo development to investigate biological factors that influence the results of subzonal injection.