There are many imaging modalities available for studying thyroid and parathyroid masses. For the thyroid gland, the demonstration of a hyperfunctioning or purely cystic mass by scintigraphy and ultrasound reassures that a palpable nodule is not cancer. Solitary, cold, or solid nodules often requires biopsy because of suspicion of malignancy. Metabolic and inflammatory disorders are imaged best with nuclear medicine studies whereas congenital thyroid lesions are evaluated best with computed tomography or MR imaging. In the search for a parathyroid adenoma, MR imaging and technetium-99m sestamibi studies appear to be most accurate, but because of its low cost, ultrasound has a favorable role. In previously operated patients with persistent hyperparathyroidism, MR imaging is probably most useful, but multiple imaging studies may be needed for definitive localization of adenomas.