Objective: To determine the utility of several perioperative adjuncts for parathyroid localization during parathyroid surgery, we prospectively compared the accuracy of sestamibi-single photon emission computed tomography (SPECT) scanning, radioguided surgery, and intraoperative parathyroid hormone (ioPTH) testing. Summary and Background Data: Minimally invasive parathyroidectomy (MIP) is rapidly becoming the procedure of choice in patients with primary hyperparathyroidism (HPT). Several perioperative adjuncts can be used to localize parathyroid adenomas, including sestamibi-SPECT scanning, radioguided surgery, and ioPTH testing. However, the relative value of each of these technologies is unclear. Methods: Between March 2001 through September 2004, 254 patients with primary HPT underwent parathyroidectomy. All patients had preoperative imaging studies and underwent radioguided surgery with a gamma probe and ioPTH testing. The use of each perioperative adjunct was determined based on the intraoperative findings. Results: The mean age of patients was 61 ± 1 year. The mean calcium and parathyroid hormone levels were 11.4 ± 0.1 mg/dL and 136 ± 6 pg/mL, respectively. Of the 254 patients, 206 (81%) had a single parathyroid adenoma, 28 (11%) had double adenomas, 19 (8%) had hyperplasia, and one had parathyroid cancer. All resected parathyroid glands were hypercellular (mean weight = 895 ± 86 mg). The cure rate after parathyroidectomy was 98%. The positive predictive values for sestamibi scanning, radioguided surgery, and ioPTH testing were 81%, 88%, and 99.5%, respectively. Conclusions: This series is one of the largest to date that prospectively compares the use of sestamibi scanning, radioguided surgery, and ioPTH testing. Of all the perioperative adjuncts used during parathyroid surgery, ioPTH testing has the highest sensitivity, positive predictive value, and accuracy. Thus, the inherent variability of sestamibi scanning and radioguided techniques emphasizes the critical role of ioPTH testing during parathyroid surgery. Copyright © 2005 by Lippincott Williams & Wilkins.