Background: In patients with primary hyperparathyroidi sm (PHPT), circulating concentrations of intact parathy roid hormone (PTH) decline dramatically within minutes following surgical excision of hyperfunctioning parathyroid tissue. The magnitude of this decay correlates with the com pleteness of resection of hyperfunctioning parathyroid tissue and can be monitored during the operation. Method: Intraoperative Quick PTH (QPTH) monitoring and pitfalls of more than 350 patients, who were operated because of primary hyperparathyroidism are analyzed. Special attention is given to correct baseline values and interpretation of QPTH values. Results: QPTH monitoring is able to distinguish reliably between single and multiple gland disease and is an indi spensable prerequisite for any form of limited parathyroid exploration. Experience with QPTH monitoring is neces sary to achieve the excellent results known from bilateral neck exploration. Conclusion: Applying correct baseline values and cautious interpretation of QPTH values results in excellent results. Nevertheless more data must be collected to allow reliable interpretation of QPTH monitoring in all patients with PHPT.