Parathyroid cancer is an extremely rare cause of primary hyperparathyroidism, accounting less than 1% of cases. The neoplasm is detected in people 40-50 years old. Ratio of men and women is 1: 1, in contrast to hyperparathyroidism caused by adenoma of epithelial bodies, when there are 3-4 times more women than men among the patients. Due to the rarity of this disease, surgeons and morphologists may have difficulties in verification of the tumor. Distinctive features of the course of the disease include the extremely rapid progression of bone changes, the development of hypercalcemic crises with a high level of blood calcium and serum parathyroid hormone. Radical surgery involves the removal of malignant parathyroid tumor in a single block with the ipsilateral thyroid gland, as well as paratracheal lymph nodes. The aim of investigation is to show a rare observation of bone manifestations of parathyroid cancer. Material and methods. Parathyroid cancer was diagnosed in 2 (0.7%) of 283 patients with primary hyperparathyroidism, operated in the Center of Endocrine Surgery. Male 29 years old was operated on in January 2016. Disease duration was about 2 years. The clinical picture was characterized by multiple bone fractures, generalized cystic osteodistorofy, renal failure, severe electrolyte disorders, cachexia. The diagnosis was confirmed by high values of total calcium and blood parathyroid hormone. The patient underwent removal of the parathyroid tumor, during the histological and immunohistochemical study of which parathyroid cancer was verified. The patient was able to sit on his own after 3 months, get up with support after 6 months and walk with the help 10 months later after the operation. In May 2017 an increase of parathyroid hormone to 1900 pg / ml was detected with a normal value of blood calcium, which indicates recurrence of parathyroid cancer. Findings. The high grade of the disease is due to both the aggressive course of parathyroid cancer and the late diagnosis.