Recent studies have shown that the injection of spermatid cells into the human oocyte can result in normal fertilization, embryo development and even delivery of live, healthy offspring. In our study, 23 azoospermic cases with severe spermatogenetic defects in their testicular biopsy are presented. The serum follicle stimulating hormone (FSH) concentrations and histopathological results of these males have been documented and compared in terms of fertilization and embryo development. The mean FSH value of the azoospermic males was 15.8 +/- 2.3 mIU/l, ranging from 1.6 to 39 mIU/l. Elongated spermatids were used in three cases only, as these more mature forms were mostly present in the testicular sample. In the remaining 20 cases, only round spermatids were found for use in intracytoplasmic sperm injection (ICSI). The fertilization rate with two pronuclei was 31.3%. The fertilization rate was found to be as high as 71% in three patients in the elongating and elongated spermatids group and as low as 25.6% in the round spermatid group. A few immature, non-motile spermatozoa were seen in only two cases from the elongated spermatid group. However, in the remaining cases, no spermatozoa were observed. The number of pronuclear (PN) arrest was quite high when only round spermatids were used (36.1%). Total fertilization failure was observed in two cases from the round spermatid group with Sertoli cell only and germ cell aplasia. A total of three pregnancies was achieved in 23 cases (13.0%), two from the elongated spermatid group and one from the round spermatid group. One biochemical pregnancy with a round spermatid resulted in an early spontaneous abortion and surprisingly, the remaining pregnancies were achieved with elongated spermatids resulting in multiple pregnancies. One twin and one triplet pregnancy were established following four embryo transfers in each patient. The twin pregnancy resulted in a live birth with two healthy babies; unfortunately, the triplet pregnancy ended in an abortion at 11 weeks. The use of testicular spermatids in the treatment of non-obstructive azoospermia may give hope by offering a novel treatment model. In cases with very severe spermatogenetic defect, even multiple pregnancies can be achieved with elongated spermatid cells by yielding a high implantation rate. However, the efficiency of round spermatids in achieving fertilization and pregnancy was disappointing.