The intent for this study is to do a retrospective chart review of all patients who have undergone minimally invasive parathyroidectomy for primary hyperthyroidism. All data collected will be recorded under assigned identification numbers that will have no association with medical record or hospital numbers. Identifying characteristics will include age and sex. Anonymity will be upheld. The patient/family will not be contacted directly. All information will be obtained from the medical chart. Demographics, location, preoperative PTH levels and intraoperative Ex-Vivo gamma counts, co-morbid conditions, and the outcome based on the hospital notes will be obtained from patients' charts and will be transferred to a secure database. It is our hypothesis that there is a linear relationship between immediate preoperative parathyroid hormone (PTH) levels and Ex-Vivo gamma counts and the aim of this study is to better describe this relationship.