Objective: To study the effect of freezing on early stage embryos derived from intracytoplasmic sperm injection (ICSI) or from IVF. Design: Prospective, controlled clinical study. Setting: Private IVF center. Patient(s): Sixty-seven consecutive patients undergoing frozen-thawed embryo transfer cycles. Intervention(s): Early stage embryos were frozen, thawed, and transferred. Main Outcome Measure(s): Post-thaw survival, implantation and pregnancy rates. Result(s): We noted an 88% post-thaw survival rate, an 18% implantation rate, and a 52% pregnancy rate in the ICSI group and 81%, 11%, and 25%, respectively, with conventional fertilization. Conclusion(s): Early stage embryos (either zygote or 2-4 cells) derived from ICSI can be frozen with confidence and higher post-thaw survival and pregnancy rates can be achieved when compared with those from conventional IVF.