Objective: To compare the results of intracytoplasmic sperm injection (ICSI) and embryo transfer (ET) cycles in men with severe oligoospermia and non-obstructive azoospermia. Materials and Methods: This study included 91 ICSI cycles performed due to male factor infertility. Patients are divided into two groups according to source of spermatozoa. Group 1 consisted of 38 cycles in which sperm was obtained from testicles (cases with non-obstructive azoospermia). In Group 2, 53 consecutive cycles were included in which ejaculated sperm was available for ICSI in spite of severe oligospermia (< 100,000/ml). Fertilization, embryo quality and clinical pregnancy rates were compared between the groups. Results: Although, the female age and mean number of oocytes retrieved were similar among the two groups, fertilization rate was significantly lower in the non-obstructive azoospermia (34.6%) group compared to group in which patients underwent ICSI with ejaculate spermatozoa (55.3%) (p < 0.05). However, there were no differences regarding mean number of available grade 1 embryos on day 3 and pregnancy rate between the two groups. Conclusion: Testicular sperm from non-obstructive azoospermia patients had significantly lower fertilization rates than the ejaculated spermatozoa from severe oligospermia patients in ICSI cycles. However, it did not bring about improved pregnancy rate.