A family (a brother and a sister) of the familidal isolated hyperparathyroidism (FIH) was reported. The older brother with age of 58 year-old was pointed out hypercalcemic while examining his hypertension and proteinuria. He had high levels of serum total and ionized calcium, intact-PTH and gastrin, and hypophosphatemia. His neck CT scan revealed swelling of the two parathyroid glands in each side. He underwent resection of the tumors and the auto-implantation of the glands under diagnosis of primary hyper parathyroidism. Histopathology was diagnosed to be hyperplasia of the parathyroid glands. The younger sister with age of 52 year-old was referred to our clinic because she was suffering from recurrent urolithiasis. Biochemical examination of her blood sampling resulted in very resemble values of her brother mentioned above. Her neck CT scan showed three tumors consisting of each one at the bilateral parathyroid glands and one in the thymic region. She underwent resection of the tumors and the auto-implantation of the glands and histopathological diagnosis was hyperplasia as same as her brother's one. The postoperative courses of these cases have been uneventful for four years. FIH is a low significant disease of which ten lineages have been reported in Japanese literature although it should be differentiate with such a disease of multiple endocrine neoplasms.