A group of patients with diagnosed primary hyperparathyroidism (PHP) in Auckland between 1982 and 1986 is reviewed. Of the 119 patients, 55 had pre‐operative scanning, 36 had no scanning prior to surgery and 29 were managed conservatively.Of the 52 patients who had pre‐operative localization with ultrasound scanning, only 27 (52%) had their adenoma correctly predicted upon neck exploration. Of the 14 patients investigated with thallium‐201 and technetium‐99m (Tl/Tc) subtraction scanning, 10 (71%) had their adenoma positively identified in the predicted locations, whereas the cause of the parathyroid pathology was correctly identified in 33 of the 36 patients (92%) who had surgery alone with no pre‐operative scanning.In 11 patients both ultrasound and Tl/Tc subtraction scanning were employed. In eight patients the results of the two scanning modalities agreed, and in seven of these eight patients the adenoma was correctly predicted (six single adenomas and one with double adenoma). In the three patients in whom the results of the two modalities differed, the Tl/Tc subtraction scanning correctly predicted the site of the adenoma in two patients and in the third patient (with a small 223 mg adenoma) both modalities were incorrect.Of the six patients with histologically proven parathyroid hyperplasia, only three had pre‐operative localization with ultrasound alone, and all three had incorrect predictions (one false positive for adenoma, and two false negative scans).Overall the results cast doubt over the usefulness of pre‐operative scanning as a routine investigation prior to initial neck exploration for primary hyperparathyroidism. However Tl/Tc subtraction scanning in particular may be useful in aiding surgical decision making for patients undergoing ‘redo’ neck exploration. Pre‐operative scanning was unhelpful in detecting hyperplasia. In the detection of adenomas Tl/Tc subtraction scanning was superior to ultrasound (71% vs 52%), but when both scanning modalities were employed, and both yielded the same results, the position of the adenoma was correctly predicted in seven out of eight cases. The results also emphasize the importance of the 24 h urinary calcium determination as part of the work‐up of the h