A 53-year-old woman presented a clinical picture of hypercalcemia as the first and most prominent manifestation of hyperthyroidism. The possibility of a coexistent hyperparathyroidism was excluded, as well as any other potential cause of hypercalcemia. The hypercalcemia and its clinical manifestations disappeared a month after the antithyroid therapy was started. After 2 years, the calcemia and renal and thyroid functions continue normal. The association of hyperthyroidism and hypercalcemia is well known, but only rarely is hypercalcemia responsible for prominent clinical symptoms. It is very infrequent for the manifestations of hypercalcemia to precede those of hyperthyroidism.