A comprehensive study is presented of a series of 124 infertile men undergoing testicular sperm retrieval for intracytoplasmic sperm injection (ICSI). In this study we correlated the histological changes observed in the testicular tissue with the results of the wet preparation and the outcome after ICSI using testicular spermatozoa. In all patients with normal spermatogenesis and hypospermatogenesis spermatozoa were recovered from the wet preparation. The sperm recovery rate as 84% in patients with incomplete germ-cell-aplasia and maturation arrest, while in patients with complete germ-cell aplasia or maturation arrest this figure was 76%. In these patients more specimens were sampled and fewer spermatozoa were recovered. Since no spermatozoa were recovered in only 10 patients, ICSI with testicular sperm was performed in the remaining 114 couples (91.9%). The normal fertilization rate was 57. 8%. The fertilization rate was significantly lower in couples among whom the husband showed germ-cell aplasia and maturation arrest. Overall, 55.2% of normally fertilized oocytes developed into embryos showing <=50% of anucleate fragments. There were no major differences between the different histological categories in terms of embryonic development in vitro. The overall pregnancy rates per testicular sperm extraction (TESE) procedure, per ICSI procedure and per transfer were respectively 36.3, 39.5 and 43.7%. The overall implantation rate per embryo (sacs/embryos replaced) was 20.3%. A lower implantation rate was observed in couples among whom the husband had maturation arrest (not statistically significant). The above data show that testicular biopsies may have an important therapeutic role in the management of infertility in azoospermic patients.