A 75-year-old woman was admitted to our hospital because of general fatigue. She had suffered from sarcoidosis during her 40s with remission, but subsequently she experienced progression of hypercalcemia and renal dysfunction for 7 years. On admission, she showed marked hypercalcemia (up to 15.5 mg/dl) and renal failure (serum creatinine 2.5 mg/dl). Plasma intact PTH level was elevated (up to 190 pg/ml), and thyroid ultrasonography and (99m) Tc-MIBI scintigraphy detected a parathyroid mass, which was surgically removed and histologically confirmed to be a parathyroid adenoma. However, even after surgery her serum calcium remained elevated, but subsequent administration of glucocorticoid for sarcoidosis completely normalized her hypercalcemia. The simultaneous occurrence of primary hyperparathyroidism and sarcoidosis is rare, and our data suggest that high plasma PTH and 1,25(OH)D exerted an additive effect on the occurrence of severe hypercalcemia.