To determine the success of intracytoplasmic sperm injection for severe male infertility. A retrospective survey. A tertiary infertility service. One hundred fourteen couples had 119 intracytoplasmic sperm injection treatments because of previous failure of standard IVF, poor results with subzonal insemination, sperm concentration < 2 x 10(6)/mL, other sperm defects, or male genital tract obstruction. Fertilization, implantation, and pregnancy rates. Of 1,185 oocytes treated by intracytoplasmic sperm injection, normal fertilization and cleavage occurred in 717 of 1,073 that survived (67% normal fertilization rate). Abnormal fertilization occurred in 113 oocytes (11% abnormal fertilization rate) and 112 oocytes did not survive the procedure (survival rate of 90%). In 117 couples, 251 embryos were transferred fresh, 409 embryos were cryopreserved, and 224 were transferred after thawing. The implantation rate was 7.4% (fetal heart per embryo transferred). To date 36 clinical pregnancies have been achieved (12% per fresh transfer, 20% per frozen transfer, and 30% overall), 24 are ongoing or delivered (6% per fresh transfer, 14% per frozen transfer, and 20% per intracytoplasmic sperm injection). The fertilization rates were the same (65%) with various sperm defects but higher with genital tract obstructions (75%). Intracytoplasmic sperm injection has improved the prognosis of severe male infertility.