© 2016 Elsevier Inc. All rights reserved. Background Vitamin D deficiency is common in patients with hyperparathyroidism, but the importance of replacement before surgery is controversial. We aimed to evaluate the impact of vitamin D deficiency on the extent of resection and risk of postoperative hypocalcemia for patients undergoing parathyroidectomy for primary hyperparathyroidism. Methods We identified patients with primary hyperparathyroidism undergoing parathyroid surgery between 2000 and 2015 using a prospectively maintained database. Patients with normal (≥30 ng/mL) vitamin D were compared to those with levels less than 30 ng/mL. Results There were 1015 (54%) patients with normal vitamin D and 872 (46%) patients with vitamin D deficiency undergoing parathyroidectomy for primary hyperparathyroidism. Vitamin D deficiency was associated with higher preoperative parathyroid hormone (median 90 versus 77 pg/mL, P < 0.001) and calcium (median 10.5 versus 10.4 mg/dL, P < 0.001) compared with normal vitamin D. To achieve similar cure rates, patients with vitamin D deficiency were less likely to require removal of more than one gland (20% versus 30%, P < 0.001) than patients with normal vitamin D. Patients with vitamin D deficiency had similar rates of persistent (1.5% versus 2.0%, P = 0.43) and recurrent (1.7% versus 2.6%, P = 0.21) hyperparathyroidism. Postoperatively, both groups had equivalent rates of transient (2.3% versus 2.3%, P = 0.97) and permanent (0.2% versus 0.4%, P = 0.52) hypocalcemia. Conclusions Restoring vitamin D in deficient patients should not delay the appropriate surgical treatment of primary hyperparathyroidism. Deficient patients are more likely to be cured with the excision of a single adenoma and no more likely to suffer persistence, recurrence, or hypocalcemia than patients with normal vitamin D.