The successful diagnosis and surgical treatment of primary hyperparathyroidism due to parathyroid adenoma benefits significantly, in our experience, from a process of pre-operative imaging localization of the parathyroid adenoma. This prospective study evaluates a window of 25 consecutive patients who underwent pre-operative imaging localization prior to successful unilateral parathyroidectomy for parathyroid adenoma. All parathyroid adenomas were successfully localized by imaging, and subsequently documented photographically in surgical correlation, and pathologically confirmed. All patients were cured biochemically. Ultrasound accurately localized 92% of adenomas (100% in the neck and extrathyroidal) while radionuclide subtraction scanning identified 60% of a smaller subset. Both DSA and CT were successful in the two cases utilized, and MRI demonstrated four of five adenomas. The high yield of these pre-operative localization studies should make them an important consideration in the routine evaluation of patients undergoing surgery for possible parathyroid adenoma. Their usefulness in directing a conservative unilateral operation may result in time and cost savings, as well as reduced surgical exposure.