Parathyroid cancer is a rare disease, causing 0.5% to 5.2% of primary hyperparathyroidism cases. Hyperparathyroidism accompanying a cancer is usually more severe with richer clinical symptomatology then hyperparathyroidism in the course of benign lesions. Every palpable neck tumour with high blood plasma calcium level should suggest the presence of parathyroid cancer. Development of cancer is slow but life prognosis depends on the extent of the first surgery. The prognosis is most favourable in case of 'en bloc' resection of tumour during the first surgical procedure. Therefore, diagnosis of cancer before operation is very important. If the surgery fails, the treatment should be aimed at lowering hypercalcaemia, which is the most common cause of the fatal sequel.