The increasing use of automated blood chemistry screens for serum calcium levels along with improved methods in measuring parathyroid hormone (PTH) levels have made the diagnosis of parathyroid disease a common clinical problem. Parathyroid adenomas account for the majority of primary hyperparathyroidism with diffuse hyperplasia and parathyroid carcinoma occurring less frequently. Early scintigraphic techniques to identify enlarged parathyroids used selenomethionine-75 which was considered to be incorporated into PTH. In general, the sensitivity of scanning the neck using this tracer was related to the size of the enlarged parathyroid, but in large series, the overall sensitivity was less than 50%. Recent work by Ferlin et al, using a Technetium-99m/Thallium-201 subtraction scintigraphic technique has yielded a sensitivity of 92% in identifying pathologically enlarged parathyroid glands. Winzelberg et al modified this technique to allow imaging the mediastinum plus simplifying the subtraction method. In a prospective study with high-resolution sonography, similar sensitivities and specificities were found with sonography and scintigraphy. Tl-201/Tc-99m pertechnetate subtraction scintigraphy appears to be an accurate technique in identifying pathologic parathyroid enlargement. Its ultimate role in the evaluation of patients with suspected hyperparathyroidism still needs to be determined.