Purpose: To determine in cases of unexplained infertility whether conventional oocyte insemination vs intracytoplasmic sperm injection results in differences in fertilization rates, frequency of failed fertilization, clinical and live delivered pregnancy rates, and implantation rates. Methods: Retrospective evaluation of these parameters in couples undergoing in vitro fertilization embryo transfer (IVF-ET) (minimum 2 embryos) in women with unexplained infertility over a 7-year period. Results: There was a significantly higher fertilization rate (p < .001) with ICSI vs conventional insemination (73.7% vs 63.7%). However of greater clinical importance, the clinical and live delivered pregnancy rates were significantly higher with conventional insemination (52.7% and 46.2%) than with ICSI 33.6% and 29.0%. The implantation rates were also significantly higher with conventional oocyte insemination (24.9% vs 17.8%). Failed fertilization was low in both groups. Conclusions: The process of ICSI, whether it involves possible subtle oocyte damage by the procedure or the andrologist not choosing the ideal sperm, may lead to embryos that are less hearty despite their normal appearance.