Introduction: Primary hyperparathyroidism is the most common cause of hyperparathyroidism and hypercalcemia, and the treatment is mainly surgical. Planning for focused surgical parathyroidectomy or minimally invasive parathyroidectomy requires precise preoperative localization of parathyroid lesions in patients with hyperparathyroidism. The purpose of this study is to evaluate reliability in correctly detecting parathyroid lesions by SPECT-CT, SPECT and planar 99mTc-Sestamibi imaging.Methods: 65 patients with primary hyperparathyroidism were enrolled in this study. All patients underwent planar and SPECT-CT before surgery. Planar imaging was performed at 20 minutes and 2 hours after injection. SPECT as well as combined non-contrast-enhanced low dose CT scan using a hybrid SPECT-CT instrument were also obtained immediately after early phase planar scintigraphy. Three image sets (early and delayed planar images, SPECT, and SPECT-CT) were reviewed for parathyroid lesion localization separately.Surgical location and histopathologic findings were used as the standard. Sensitivity and positive predictive value were determined for each method.Results: In all patients (5 cases with multiple endocrine neoplasia), surgery was done successfully. Totally, 72 parathyroid lesions (70 adenomas and 2 hyperplasia) were dissected. Solitary parathyroid adenoma, double parathyroid adenomas, and double hyperplastic parathyroid glands were found in 60, 5, and 1 patients, reSPECTively. Planar images showed correct localization of lesions only in 36 cases, with low sensitivity (63%) and positive predictive value (69%) in comparison with other image sets. Sensitivity of SPECT-CT (88%) was significantly greater than SPECT (72%) (p>0.001). Positive predictive value of SPECT- CT (92%) was also greater than SPECT (80%) (p>0.001). SPECT-CT was markedly superior to planar images and SPECT in patients with ectopic adenomas.Conclusion: In patients with primary hyperparathyroidism preoperative SPECT-CT is a reliable method for parathyroid lesion localization, and is also helpful in surgical planning for parathyroidectomy.