Introduction & Objective: Azoospermia means no sperm in semen. It may be due to hormonal imbalance, any disorder in production of sperm, or might be due to obstruction in sperm pathway from testis till ejaculatory ducts. This study was performed to determine the causes of azoospermia in infertile male, referred to Yasuj clinic of urology.Material & Methods: This study was done during more than 2 years beginning from May 2004. Patients with at least two consecutive azoospermic semen analyses were included in this study after a complete history taking, physical examination, hormonal study (FSH, LH, prolactine, testosterone), vasography, testis biopsy and genetic evaluation.Results: Among 842 infertile men, 172 patients (20.4%) were azoospermic. 28 patients (16.3%) with obstructive azoospermia and 144 patients (83.7%) with non obstructive azoospermia were detected. Common causes of non obstructive azoospermia were as follow: idiopathic 68 patients (39.53%), atrophied testes 40 patients (23.25%), sertoli cell only 34 (19.76%) patient, undescended testes 28 (16.27%) patients and post chemotherapy in 2 (1.16%) patients. Causes of obstructive azoospermia were obstruction of epididymis or vasa deferens in 24 patients (86%) and congenital bilateral agenesis of vasa deferens in 4 patients (14%).Conclusion: Results of this study showed that about 20% of infertile men are azoospermic and the most common type of azoospermia is non obstructive type.