Klinefelter's syndrome is one of the most common forms of primary hypogonadism 
and infertility in males. It is characterized by small and firm testes, 
gynecomastia, azoospermia, and an elevated gonadotropin level. The frequencies 
of diabetes mellitus, breast cancer, and germ cell neoplasia increases in 
Klinefelter's syndrome. We report upon a 35 year-old male patient with Graves' 
disease in association with Klinefelter's syndrome; as confirmed by chromosome 
analysis. The patient is being treated with antithyroid medication for Graves' 
disease and by testosterone replacement for Klinefelter's syndrome.