The value of high-resolution real-time ultrasonography in locating parathyroid adenomas was compared with that of computed tomography (CT). In 21 patients with a single parathyroid adenoma verified at neck exploration, preoperative ultrasonography and CT detected the adenoma in 15 and 11 cases, respectively. Ultrasound gave false-positive results in four patients and false-negative in two, whereas CT was false-positive in four patients and false-negative in six. Most false-positive reports were due to misinterpretation of small thyroid nodules. For acceptable accuracy both methods require an experienced radiologist. Technical and interpretive problems seem to be somewhat less frequent with ultrasonography than with CT. Ultrasonography has therefore become the method of choice for preoperative location of enlarged parathyroid glands at our hospital, and CT is used as a complementary procedure, e.g. when a mediastinal adenoma is suspected.