The dual tracer nuclear scintiscan using technetium and thallium to localize enlarged or ectopic parathyroid tissue has been reported to be highly accurate and efficacious. Fourteen previous series reporting results of the technique have been compiled from the literature and analyzed. This analysis has revealed a total of 317 surgically confirmed scan results with a low false-positive rate (17 of 317 scans), a sensitivity rate of 82 percent, and an overall accuracy rate of 78 percent. Forty-five patients from five Portland area hospitals have been retrospectively studied. They had a total of 49 preoperative scans. In our experience with the scan, a higher false-positive rate (4 of 45 scans), a sensitivity rate of 78 percent, and an overall accuracy rate of 73 percent were noted. The scan's effectiveness in acknowledged areas of difficulty in parathyroid surgery, such as patients with ectopic adenomas, hyperplastic glands, and those with previous neck explorations, has been analyzed. We conclude that the scan is a useful preoperative localization tool, especially in patients with ectopic adenomas or with persistent hypercalcemia after neck exploration. However, it is less accurate than initially reported in complex patients, and additional localization techniques are frequently required.