Case report of a patient with hypercalcemia and suspected parathyroid adenoma. Because of a previous strumectomy a precise preoperative localization of the suspected parathyroid adenoma was demanded. Tc-99m-tetrofosmin scintigraphy in double phase technique failed to detect a parathyroid adenoma by failing to show a region of increased focal uptake with delayed washout in relation to the thyroid gland. Only comparison of the Tc-99m-tetrofosmin images with a Tc-99m-pertechnetate scan revealed a right caudal parathyroid adenoma. A double phase Tc-99m-MIBI study of the same patient was able to localize this parathyroid adenoma without the need of a corresponding Tc-99m-pertechnetate scintigraphy due to a differential washout with persistent focal uptake in the parathyroid adenoma and a progressively decreasing uptake in the thyroid tissue. This case indicates that Tc-99m-tetrofosmin is a suitable agent for parathyroid imaging only if used together with Tc-99m-pertechnetate but it seems to lack the differential washout characteritics of Tc-99m-MIBI according parathyroid gland and thyroid gland.