In recent years, several series have documented the feasibility of endoscopic approaches for parathyroid diseases. We performed a retrospective study to evaluate the results of endoscopic parathyroidectomy (EP) in the management of our patients with primary hyperparathyroidism (PHPT). During a 5.5 year period (1998-2003), we operated on 644 patients with PHPT. EP was proposed for patients with sporadic PHPT, without associated goiter, and without previous neck surgery in whom a single adenoma was localized by means of sonography and sestamibi scanning. EP was performed by the lateral approach with insufflation for patients with an adenoma located deep in the neck and by a gasless midline approach for patients whose adenoma was located anteriorly. A quick parathyroid (QPTH) assay was used during the surgical procedures. Among 644 patients with PHPT, 279 (43.3%) were not eligible for EP for the following reasons: associated nodular goiter (116 cases), previous neck surgery (52 cases), suspicion of multiglandular disease (31 cases), lack of preoperative localization (61 cases), and miscellaneous causes (19 cases). EP was performed in 365 patients with sporadic PHPT: 339 lateral access, 25 midline access, and one thoracoscopy. The median operating time was 49 minutes (16-130 minutes). Conversion to conventional parathyroidectomy was required in 49 patients (13.4%) for these reasons: missed adenomas (14 cases), difficulty with the dissection (8 cases), multiglandular disease correctly predicted by QPTH (11 cases), false-negative QPTH assay results (4 cases), false-positive sestamibi scan results (11 cases), and 1 false-positive sonography result. One patient presented with definitive recurrent nerve palsy. Three patients remained hypercalcemic, and one other patient had recurrent hypercalcemia. In conclusion, EP can be proposed for more than half of the patients with PHPT. Immediate results of EP are similar to those obtained with conventional parathyroidectomy, but no conclusions can be drawn in terms of the influence of EP on the outcome of the patients operated on for PHPT.