A 49 year-old Japanese woman had subjected enlargement of a cervical tumor, and also suffered two bone fractures in 2 years. The cervical tumor had enlarged further in the month prior toadmission, becoming warm and tender. Endocrinological examination revealed that the serum intact PTH concentration was remarkably high at 400 pg/mL despite the low serum calcium concentration, and that the serum vitamin Ds concentration was decreased. Bone roentgenograms revealed severe osteolytic changes compatible with osteitis fibrosa cystica and a pathologic fracture of the humerus.Under a diagnosis of primary hyperparathyroidism, parathyroidectomy was performed, followed by fixation surgery for the pathologic fracture. Histologically, the cervical tumor was a parathyroid chiefcell adenoma with massive necrosis, and the bone pathology by iliac bone biopsy revealed the existence of osteomalacia. She was treated with calcium, vitamins D and K2 and calcitonin after the surgery. This case is a rare condition manifesting hypocalcemia with catastrophic osteoporosis under the coexistence of spontaneous infarction of parathyroid adenoma with osteomalacia, suggesting that the clinical features of hyperparathyroidism are modified by both the autoparathyroidiectomy and the existence of osteomalacia due to vitamin D deficiency.