In a non prospective study the value of preoperative parathyroid imaging with 99mTc-MIBI-scintigraphy was evaluated.From August 1, 1987 to December 15, 1997 453 patients were operated on for hyperparathyroidism. Preoperatively 116 patients underwent 99mTc-MIBI-scanning, which had been carried out by several institutes.Primary hyperparathyroidism. Sensitivity of MIBI-scintigraphy in solitary parathyroid adenoma (n = 48) and first-time cervical exploration was 54% (25 true positive scans) and overall sensitivity was 50% (25 true positive scans in 53 patients). In 6 patients with persistence or recurrence of primary hyperparathyroidism MIBI-scintigraphy was true positive (sensitivity 100%). Neither the volume nor the weight of the adenomas influenced the result of MIBI-scanning. There was no correlation between preoperative serum concentrations of calcium and intact parathormone and sensitivity of MIBI-scintigraphy. Renal hyperparathyroidism. Before first-time cervical exploration sensitivity of MIBI-scintigraphy (n = 40) for detecting all abnormal parathyroid glands in the presence of diffuse hyperplasia yielded only 10%. In 5 of 7 patients, who underwent reexplorations of the neck or mediastinum for persistence or recurrence of renal hyperparathyroidism MIBI-scintigraphy was true positive (sensitivity 71%). The sensitivity for detection of hyperplastic parathyroid glands correlated with the weight as well as with the volume of the glands (p 90% sensitivity.