[31-year-old male patient with testicular mass and hyperthyroidism].

An excess of human chorionic gonadotropin (hCG) is a rare differential diagnosis of hyperthyroidism, due to the TSH-like effect of hCG. hCG levels physiologically increase during pregnancy. In patients with germ cell tumors of the testicles and the ovary, a pathological increase of hCG serum concentrations may also be found, depending on the histological subtype. We report on a 31-year-old male patient with overt clinical hyperthyroidism resulting of a hCG-producing metastasized germ cell tumor of the right testicle. After initiation of chemotherapy, thyroid function normalized in parallel to the tumor's remission with marked decrease of hCG levels.