A case of 35-year-old woman with parathyroid cancer is presented. Five years ago she underwent surgery for follicular thyroid cancer. Parathyroid cancer was evidenced by palpable, solid, irregularly shaped cervical tumor 5 cm in diameter. The patient had severe hyperparathyroidism confirmed by biochemical findings of hypercalcemia reaching 16 mg%, hypophosphatemia and hyperphosphatasemia. Serum parathormone level was 23-fold higher than the norm. These findings were accompanied by polyuria, polidypsia, symptoms of bone damage and renal calcification. After the surgery the patient's condition improved significantly despite persistent hyperparathyroidism. The level of parathormone decreased, but was still 11 times higher than the norm. Two months after the surgery she noticed a single node on her neck. The patient was re-operated for recurrence of parathyroid cancer. Serum parathormone level was then 6-8 times above the norm. Medical treatment with furosemide, calcitonin and biphosphonate resulted in normalization of calcemia and phosphatemia. Further management will aim at localization of foci of hyperactive parathyroid tissue in order to enable radical reoperation. The case is reported because of rare occurrence of parathyroid carcinoma as well as because the carcinoma occurred in a patient who previously had follicular thyroid cancer. There are no reports of coexistence of these two neoplasms in available literature.

Keywords: parathyroid cancer, primary hyperparathyroidism and non-medullary thyroid cancer