In the preoperative setting, all patients with suspected hyperparathyroidism on laboratory and clinical evaluation in whom surgical intervention is being considered are candi­dates for neck ultrasound. In cases of primary hyperparathy­roidism (80% of which are attributable to a single adenoma), ultrasound is often critical to precisely localizing the enlarged gland [23]. Identifying relationships of the gland to normal neck structures can then facilitate a minimally invasive para­thyroidectomy (Fig.13.1). Primary parathyroid hyperplasia is suspected when both the ultrasound and sestamibi scan fail to identify a candidate adenoma, as multiple hyperplastic glands may be too small for detection by either imaging modality. Similarly, because hyperplastic change is often asymmetric, the identication of more than one candidate gland on ultrasound can also indicate primary hyperplasia (Fig.13.2). In either case, these features prepare the surgeon for the possibility of a bilateral exploration. In patients with suspected secondary or tertiary hyperparathyroidism, in whom multigland hyperplasia is expected, ultrasound may often detect enlarged glands (Fig.13.3). The order of explo­ration can then be determined based on gland size, with the potential aid of intraoperative PTH levels.