The most common cause of primary hyperparathyroidism (PHPT) is a single, sporadic parathyroid adenoma. Ultrasonography (US) and (99m)Technetium methoxyisobutylisonitrile (Tc-99m-MIBI) scintigraphy are the imaging methods most widely used to localize parathyroid adenomas. The purpose of the present study was to determine the diagnostic value and accuracy of endoscopic ultrasonography (EUS) for localizing parathyroid adenoma compared with those of US and Tc-99m-MIBI scintigraphy. Forty-seven patients with a PHPT diagnosis and who were recommended for surgery were enrolled in this study. An endoscopist who was blinded to the previous US and Tc-99m-MIBI scintigraphy results performed the EUS in each patient. Thirty-nine female and eight male patients with PHPT were evaluated. The presence of adenoma was confirmed by subsequent postsurgical pathology results. One case was excluded because the histopathological evaluation was compatible with a lymph node, although the lesion was detected using three different imaging modalities preoperatively. The locations of the parathyroid adenomas were correctly documented by US in 39 patients (84.7 %) by Tc-99m-MIBI scintigraphy in 35 (76.0 %), and by EUS in 44 (95.6 %) of 46 patients. EUS located all 31 adenomas detected previously with US and Tc-99m-MIBI scintigraphy. EUS also successfully located three adenomas that could not be identified by US and Tc-99m-MIBI scintigraphy. The positive predictive value and diagnostic accuracy of EUS, US, and Tc-99m-MIBI were 97.7, 97.7, and 95.6 %; 88.6, 97.5, and 86.9 %; and 77.7, 97.2, 76.0 %, respectively. EUS was preferred as the second step imaging tool for detecting parathyroid adenomas that could not be localized by US and Tc-99m-MIBI scintigraphy.