Parathyroid adenomas account for most cases of primary hyperparathyroidism (1 degrees HPT). Certain symptoms and biochemical abnormalities alert the surgeon to their presence, since these benign tumors are rarely evident on physical examination. Moreover, because they are usually very small, preoperative localization using sestamibi scanning or ultrasonography is required to avoid bilateral neck exploration. Parathyroid adenomas rarely attain huge proportions. We report a case of a parathyroid adenoma measuring 8 x 5 x 3.5 cm and weighing 110 g; to our knowledge the greatest mass reported in the literature. Interestingly, despite its huge size it did not cause many of the hypercalcemic symptoms usually associated with larger adenomas, but rather it manifested with symptoms of local pressure, another unusual property of this atypical tumor.