A male factor is solely responsible in approximately 20%of cases of infertility and contributory in another 30-40%.Azoospermia is present in 15-20%of infertile males.Although the main goal of the evaluation of the infertile men is to identify the reversible conditions,to identify the irreversible causes that can or cannot be managed by assisted reproductive techniques(ART)is also important.Etiologies for azoospermia can be categorized as pre-testicular,testicular and posttesticular.Azoospermia is defined as the absence of sperm from at least two centrifuged semen samples.The initial evaluation of the azoospermia men includes a thorough history,physical examination,and hormonal tests.Physical examination should focus on testis size and presence of vas deferens and varicocele.Hormonal evaluation should include measurement of serum testosterone and follicle stimulating hormone(FSH)levels.When the vasa are palpable,testis size,semen volume and serum FSH are key factors in determining the etiology of the azoospermia.If the semen volume is reduced and this is not an artifact,the first laboratory test is post-ejaculatory urinalysis to exclude a retrograde ejaculation.After exclusion of retrograde ejaculation,transrectal ultrasonography(TRUS)should be considered to identify ejaculatory duct obstruction(EDO).Dilation of the seminal vesicles serves as a sign of EDO.Seminal vesicle aspiration to identify sperm at the time of TRUS can increase the diagnostic accuracy.In our center,TRUS-guided opacification of the seminal tracts with a mixture of contrast media and dye is performed to facilitate effective transurethral resection(TUR)of ejaculatory duct.Based on our experiences,patients with midline cysts who are treated by TUR are expected to have the best outcome.Testis size and level of serum FSH in azoospermic males with normal semen volume are critical factors in determining diagnostic strategies.Men with elevated FSH and bilateral small testis have non-obstructive azoospermia(NOA).Diagnostic testicular biopsy is not required in cases of NOA.Elevated FSH is indicative of a significant problem with spermatogenesis whereas a normal serum FSH does not guarantee intact spermatogenesis.Therefore,patients with normal testis size and FSH level should undergo a testicular biopsy to provide a definitive diagnosis.If the testicular biopsy is normal,most men have bilateral epididymal obstruction.Epididymal obstruction can be identified only by surgical exploration.Vasography is performed at the time of reconstructive surgery.Once sperm are found from the epididymal tubule,vasoepididymostomy is performed.The best results can be achieved by surgeons with training and on-going experience in microsurgery.There is some evidence that a small percentage of men with NOA may benefit from treatment of a clinical varicocele.Therefore,it is reasonable to offer men with NOA and clinical varicoceles a varicocelectomy.However,the most men will still need to use intracytoplasmic sperm injection(ICSI)to conceive.Testicular sperm extraction(TESE)should be offered to all men with NOA.Microsurgical TESE increases retrieval rates,and should be preferred in severe cases of NOA.