We report a case of 77-year-old woman who presented with lumbago and hypercalcemia. Multiple myeloma (MM) was first diagnosed by serum protein electrophoresis and bone marrow aspiration, but intact parathyroid hormone (intactPTH) was also found to be high in the presence of persistent hypercalcemia with anorexia and nausea. After lowering serum calcium with bisphosphonate administration, parathyroidectomy was performed. Upon histologic examination, the tumor was determined to be parathyroidal chief-cell hyperplasia and the patient was treated with melphalan and prednisolone. The relationship between MM and primary hyperparathyroidism (I degree HPT) remains unknown. Although the co-existence of MM and I degree HPT was reported in 12 reports from various parts of the world, there was only 1 report in Japan. The present case is an example of successful treatment for a complicated disorder, and suggests that patients suffering from bone pain or hypercalcemia need to be examined both endocrinologically and hematologically.