['To assess the efficiency of intracytoplasmic sperm injection (ICSI) using testicular spermatozoa in cases of nonobstructive azoospermia.', 'Retrospective case series.', 'Tertiary university-based infertility center.', 'Overall, 595 couples were included. In 360 couples, the man had normal spermatogenesis. In 118, 85, and 32 couples the man had germ-cell aplasia, maturation arrest, and tubular sclerosis/atrophy, all with focal spermatogenesis present.', 'We performed 911 ICSI cycles using fresh sperm obtained after testicular biopsies: 306 ICSI cycles used testicular sperm from men with nonobstructive azoospermia, and 605 ICSI cycles used testicular sperm from men with obstructive azoospermia.', 'Fertilization, cleavage, implantation, and pregnancy rates.', 'Overall, the 2PN fertilization rate was lower in the nonobstructive group: 48.5% vs. 59.7%. There were no differences in in vitro development or in the morphological quality of the embryos. In the nonobstructive group, a total of 718 embryos were transferred (262 transfers) vs. 1,525 embryos in the obstructive group (544 transfers). Both the clinical implantation rate and clinical pregnancy rate per cycle were significantly lower in the nonobstructive group compared with the obstructive group: 8.6% vs. 12.5% and 15.4% vs. 24.0%, respectively.'] Is intracytoplasmic sperm injection with testicular spermatozoa less successful in men with nonobstructive azoospermia than in men with obstructive azoospermia?