<prompt> A male with azoospermia found to have normal FSH testosterone levels normal size testes. Probable cause isVas obstructionKallman syndromeUndescended testisKlinefelters syndrome  <response>: Bilateral vas obstruction can cause azoospermia with normal FSH and testosterone levels and normal sized testis. Kallmann syndrome results from defective hypothalamic gonadotropin-releasing hormone GnRH synthesis. It is characterized by low luteinizing hormone LH and follicle-stimu- lating hormone FSH levels and low concentrations of sex steroids testosterone or estradiol. Patients with undescended testis have different FSH and LH levels with the level of sperm density and spermatogenesis. The FSH levels in men are usually inversely correlated with sperm counts and indicate the integrity of seminiferous tubules, a marker of spermatogenesis. Patients with bilateral undescended testes have significantly lower sperm motility, sperm concentration, testicular volume and inhibin B levels, while showing higher FSH and LH levels than those with unilateral undescended testis. Klinefelters Syndrome is characterized by small testes, infeility, gynecomastia, tall statureincreased leg length, and hypogonadism in phenotypic males.Plasma concentrations of FSH and luteinizing hormone LH are increased in most adults with 47,XXY, and plasma testosterone is decreased 50-75, reflecting primary gonadal failure. Reference : page 2256 and 2350 Harrisons Principles of Internal Medicine 19th edition. 