We report a case of hyperthyroidism complicating and revealing a metastatized adenocarcinoma of the stomach with high circulating levels of human chorionic gonadotropin and its beta component. To our knowledge, this is the first reported case of a non-trophoblastic tumor with hyperthyroidism and secreting quantities of these hormones. High circulating levels of beta component in such patients have been considered to be a sign of malignancy. The mechanisms of thyroid stimulation could be related to the biological activity of certain forms of the human chorionic gonadotropin.