Preoperative preparation of patients with hyperarathyroidism planned to be operated and/or already operated because of some other disease have specific characteristics in function of the type of hyperparathyroidism, primary or secondary. In primary hyperparathyroidism, repercussions of pronounced hypercalcemia on organs and systems are of essential importance. The most important aspect of preoperative preparation of these patients is therefore the treatment of hypercalcemia. In patients with secondary hyperparathyroidism as comorbidity, calcium level is of lesser importance since it stays mostly within reference values. Essential for perioperative preparation of these patients is the fact that they have chronic renal insufficiency and usually are on extrarenal depuration, so that uremic toxic disorders important for the perioperative course should be taken into account. Disorders caused by primary or secondary hyperparathyroidism (and terminal chronic renal insufficiency) must be brough to so-called "stable state" in elective surgical interventions. Preoperative preparation in urgent surgical interventions is focused only on vitally endangering consequences of hyperparathyroidism such as hypercalcemic crisis or extreme hyperkalemia.