WE REPORT the cases of three patients in whom hyperparathyroidism was strongly suspected on clinical grounds and in whom ultrasonography of the neck showed the presence of a small mass near one of the lobes of the thyroid gland, which was believed to represent a parathyroid adenoma. All three patients underwent surgery, and the diagnosis and exact location of the adenoma was confirmed. Methods The ultrasound procedures were performed with a commercially available gray-scale ultrasound unit using a 5-MHz, 6-mm diameter, nonfocused transducer. The patients were examined in the supine position, with the neck hyperextended. Multiple transverse B scans were obtained from the level of the sternal notch superiorly in 0.5-cm intervals until thyroid tissue was no longer displayed (usually at the level of the larynx). Several longitudinal scans of each side of the neck were then obtained in 0.5-cm intervals. Report of Cases Case 1.— A 39-year-old man had