We assessed fertilization, pregnancy and miscarriage rates in patients with obstructive and nonobstructive azoospermia who underwent intracytoplasmic sperm injection. From June 1996 to March 2000, 166 consecutive patients (198 intracytoplasmic sperm injection cycles) with azoospermia were studied. Of these 198 cycles 68 were performed due to nonobstructive azoospermia using testicular spermatozoa and 130 were performed due to obstructive azoospermia using epididymal spermatozoa. The normal (2 pronuclei) and abnormal (1 plus 3 pronuclei) fertilization rates for obstructive and nonobstructive azoospermia were 60.5% and 16.6%, and 54% and 16.4%, respectively (p >0.05). The pregnancy rate per cycle, pregnancy rate per patient and abortion rate were 30%, 39.8% and 28% for obstructive azoospermia, and 22%, 28.3% and 40% for nonobstructive azoospermia (p <0.05). The normal and abnormal fertilization rates were 58.7% and 21.4% for percutaneous epididymal sperm aspiration (PESA), 62.3% and 10.4% for PESA plus testicular sperm aspiration (TESA), and 57.3% and 14.5% for TESA, respectively (p >0.05). The pregnancy rate per cycle, pregnancy rate per patient and abortion rate were 34.6%, 54.5% and 11.1% for PESA, 37.5%, 37.5% and 33.3% for PESA plus TESA, and 26.1%, 31% and 41% for TESA, respectively (PESA versus PESA plus TESA p >0.05, and PESA and PESA plus TESA versus TESA p <0.05). Epididymal or testicular motile sperm resulted in a lower abortion rate than epididymal or testicular immotile sperm (p = 0.03). No differences were noted in the fertilization and embryo transfer rates irrespective of etiology (obstructive versus nonobstructive) and type of spermatozoa (epididymal versus testicular). Testicular sperm retrieval results in lower fertilization and pregnancy rates as well as higher abortion rates than epididymal sperm retrieval.