The greater the number of cases and the greater the variability in PTH decrease after thyroidectomy, the better the understanding of the role of 1,25(OH)2D. Furthermore, the most important finding of this study was that 1,25(OH)2D levels on the morning of the first postoperative day were dependent on preoperative 1,25(OH)2D levels, which was confirmed when patients with Graves’ disease and tumors were analyzed separately. This evidence concerns the gene PTH and Graves disease.