Successful parathyroidectomy for sporadic primary hyperparathyroidism (pHPT) is predicted by a 50% drop in PTH intra-operatively. Vitamin D is a known inhibitor of PTH secretion and is associated with secondary HPT following adenoma resection. This study examined the impact of 25-hydroxyvitamin D (25OHD) deficiency on perioperative PTH kinetics and outcomes following parathyroidectomy.Patients undergoing adenoma resection for pHPT (n=93) had PTH levels recorded at six perioperative time points. Preoperative 25OHD levels were examined retrospectively. Patients were considered 25OHD deficient if the level was <25 ng/mL (n=47) and adequate if the level was >or=25 ng/mL (n=46).Patients with 25OHD-deficiency had significantly higher preoperative calcium, alkaline phosphatase, and PTH levels. PTH levels were significantly higher in 25OHD-deficient patients at incision, at 1 week postop and 1-3 months postop. Average drop in PTH level five minutes post resection was 79+/-14% in the deficient group and 72+/-22% in the non-deficient group (P=.03). 25OHD levels inversely correlated with adenoma weight (P=.03) and postoperative PTH measurements (P=.008).Sporadic pHPT patients with 25OHD deficiency have higher baseline and postoperative PTH levels compared to non-deficient patients but do not have altered intraoperative PTH kinetics. Vitamin D deficiency is associated with postoperative elevation of PTH.