Minimally invasive parathyroidectomy (MIP) has become the procedure of choice in the treatment of primary hyperparathyroidism where a single adenoma can be localized preoperatively. The role for intra-operative parathyroid hormone measurement (IOPTH) is controversial. Some experts recommend that IOPTH is a mandatory requirement for successful MIP while others state that the technique is not needed. We reviewed 10 years of MIP in a single unit without the use of IOPTH in order to examine causes of failure. This study is a retrospective review of the University of Sydney Endocrine Surgery Database from May of 1998 to August of 2008. The database was queried for MIPs performed as well as for failed operations. Patient record analysis was completed to determine the reason for failure of the operation. In the period January 1998 to August 2008, a total of 2343 parathyroidectomy procedures were performed. Of these, 1020 were MIPs with 23 (2.2%) failures. One patient was found to have benign familial hypercalcemia, whereas five were lost to follow-up. Reasons for failure in the remaining 17 patients were: 10 patients (59%) were found to have double adenomas, 3 (17%) patients with hyperplasia and 4 (24%) patients with single gland disease were missed at initial operation. All 17 were cured on repeat exploration. MIP can be performed safely and with 98% success without the need for IOPTH. The most common cause of failure after MIP is an occult double adenoma. Given that repeat sestamibi scan correctly identifies persistent disease in most cases, consideration can be given to MIP as a choice of procedure for repeat operation. © 2010 The Authors. ANZ Journal of Surgery © 2010 Royal Australasian College of Surgeons.