The features of calcium, phosphorus, parathyroid hormone, vitamin D indexes in patients with diffuse toxic goiter after thyroidectomy are presented. It is set that age, greater thyroid volume, decreased 25(ОН)D level before operation, decline of parathyroid hormone level after operation it is belonged to the basic parameters that influence on development of hypocalcemia in patients with diffuse toxic goiter after thyroidectomy. 25(ОН)D level below 20 ng/ml it follows to examine as to specific and sensible preoperated predictor of hypocalcemia development after thyroidectomy as well as hypoparathyroidism.