Azoospermia may occur because of reproductive tract obstruction (obstructive azoospermia) or inadequate production of spermatozoa, such that spermatozoa do not appear in the ejaculate (non-obstructive azoospermia). Azoospermia is diagnosed based on the absence of spermatozoa after centrifugation of complete semen specimens using microscopic analysis. History and physical examination and hormonal analysis (FSH, testosterone) are undertaken to define the cause of azoospermia. Together, these factors provide a >90% prediction of the type of azoospermia (obstructive v. non-obstructive). Full definition of the type of azoospermia is provided based on diagnostic testicular biopsy. Obstructive azoospermia may be congenital (congenital absence of the vas deferens, idiopathic epididymal obstruction) or acquired (from infections, vasectomy, or other iatrogenic injuries to the male reproductive tract). Couples in whom the man has congenital reproductive tract obstruction should have cystic fibrosis (CF) gene mutation analysis for the female partner because of the high risk of the male being a CF carrier. Patients with acquired obstruction of the male reproductive tract may be treated using microsurgical reconstruction or transurethral resection of the ejaculatory ducts, depending on the level of obstruction. Alternatively, sperm retrieval with assisted reproduction may be used to effect pregnancies, with success rates of 25–65% reported by different centres. Non-obstructive azoospermia may be treated by defining the cause of low sperm production and initiating treatment. Genetic evaluation with Y-chromosome microdeletion analysis and karyotype testing provides prognostic information in these men. For men who have had any factors potentially affecting sperm production treated and remain azoospermic, sperm retrieval from the testis may be effective in 30–70% of cases. Once sperm are found, pregnancy rates of 20–50% may be obtained at different centres with in vitro fertilisation and intracytoplasmic sperm injection.