Primary hyperparathyroidism (PHPT) is classically characterized by stone and bone disease, clinical bone involvement is seldom seen nowadays (<5% of patients). In PHPT, classical skeletal involvement can be the first sign but due to rarity of its occurrence it is no longer included in the differential diagnosis of such manifestations of skeletal diseases. Radiological (X-ray and CT scan) findings of osteitis fibrosa cystica include lytic or multilobular cystic changes [brown tumors] and these lesions can be easily misinterpreted as metastatic carcinoma, oteoclastoma, fibrous dysplasia, and especially giant cell tumor that has almost same radiological and histological features if serum calcium and parathyroid hormone (PTH) are not assessed, which are elevated only in PHPT. Conclusion: When radiographic evidence of a lytic lesion and hypercalcemia are present, PHPT should always be considered in the differential diagnosis. Key messages: Primary hyperparathyroidism most often is due to a parathyroid adenoma. Due to elevated PTH levels bone resorption increases, leading to polyostotic lesions and a reduction in bone mineral density. Osteitis fibrosa cystica eventually develops in patients with advanced disease and patients often require parathyroidectomy as a definitive treatment.