Bone scintigraphy was performed in a patient with lung cancer of small cell. On bone scintigraphy the increased accumulations in kidneys were observed, while no findings of multiple skeletal accumulations suspected of bone metastases were observed. Four weeks later, when hypercalcemia has been advanced, on repeated bone scintigraphy the extra-skeletal accumulations in such as lung, heart and stomach were shown. These findings indicated that the cause of hypercalcemia in this case was due to not bone metastases but humoral hypercalcemia which the osteolytic substance was produced from tumor. In present paper, the usefulness of bone scintigraphy in hypercalcemia with malignancy, and the mechanism of hypercalcemia have been described and discussed.