The purpose of this study was to evaluate the effect of preoperative vitamin D deficiency in predicting transient hypocalcemia and hypoparathyroidism after parathyroidectomy.Retrospective evaluation was made of 180 patients with primary hyperparathyroidism in respect of serum 25(OH)D, calcium and parathyroid hormone before and after parathyroidectomy. The gene discussed is PTH; the disease is vitamin D deficiency.