Objective: to consider principles in the differential diagnosis of parathyroid osteodystrophy with skeletal metastases, as well as the tactical errors occurring in the treatment of this category of patients. Material and methods. The common biochemical principles of phosphorus-calcium homeostasis in the body and the mechanisms of primary hyperparathyroidism (PHPT) were considered. Results. The results of treatment were summarized in 22 patients aged 30 to 68 years with parathyroid adenoma; the characteristic diagnostic errors were considered. A rare clinical case of PHPT caused by lateral parathyroid adenoma was described. Conclusion. After clinical introduction of tests for the level of serum calcium and parathyroid, our view of its prevalence has been changed dramatically. Despite the fact that the symptoms of hyperparathyroidism are well-known, the clinical picture of hyperparathyroid osteodystrophy, which encompasses similar skeletal clinical and radiographically changes, is frequently associated with metastases without revealing a primary focus. For this reason, one should remember that there may be PHPT caused by benign parathyroid adenoma in most cases when both detecting hypercalcemia and suspecting skeletal metastatic involvement.