Background: Primary hyperaparathyroidism (pHPT) is often accompanied by underlying thyroid pathology that can confound preoperative parathyroid localization studies and complicate intra-operative decision making. The aim of this study was to examine the utility of preoperative thyroid ultrasonography (US) in patients prior to undergoing parathyroidectomy for pHPT.Methods: An Institutional Review Board approved prospective study was undertaken from January 2005 through July 2008. All patients with pHPT meeting inclusion criteria (n=94) underwent preoperative thyroid ultrasound in addition to standard 99mTc-sestamibi scintigraphy for parathyroid localization. Demographics, operative management and final pathology were examined in all cases.Results: Fifty-four of the 94 patients (57%) were noted to have a thyroid nodule on preoperative US, of which 30 (56%) underwent further examination with fine needle aspiration biopsy. Alteration of the operative plan attributable to underlying thyroid pathology occurred in 16 patients (17%), with patients undergoing either total thyroidectomy (n=9) or thyroid lobectomy (n=7). Thyroid cancer was noted in 33% of patients undergoing thyroid resection, and 6% of all patients with HPT.Conclusions: The routine utilization of preoperative thyroid ultrasound in patients prior to undergoing parathyroid surgery for pHPT is indicated. The added information from this non-invasive modality facilitates timely management of co-incidental, and sometimes malignant, thyroid pathology.