The indications for diagnostic testicular biopsy are patients with azoospermia or extreme oligospermia syndrome with normal testicular volume and serum FSH levels. The purpose of the biopsy is to distinguish between testicular insufficiency and male genital tract obstruction. Testicular biopsy in patients with non-obstructive azoospermia is intended to be performed as a therapeutic tool, only when sperm are obtained by ICSI. Testicular tissue obtained by testicular biopsy that contains sufficient sperm should be frozen and preserved for ICSI. The pathology is classified as follows: Sclerosing sclerosis – absence of spermatogenic tubules. Sertoli cell syndrome – only supporting cells are present in the seminiferous tubules without any spermatogenic cells. Sperm maturation disorder – incomplete spermatogenesis, impaired differentiation of spermatocytes. Reduced spermatogenesis – spermatogenesis is present, but the spermatogenic epithelium is thin and there is a uniform decrease in spermatogonia and spermatozoa at all levels. In patients who are at high risk for testicular germ cell tumors (e.g., infertility, cryptorchidism, history of testicular tumors, testicular atrophy) and testicular microcalcifications, testicular biopsy can be performed to detect testicular tumors in situ.