Parathyroid adenomas and the rare parathyroid carcinoma can be clinically mistaken for thyroid nodules. Smears are cellular, with cohesive sheets, ribbon-like cords and occasional microacini. The cells have round nuclei with a coarsely granular chromatin pattern and granular cytoplasm. Bare nuclei and isolated cells can be present. Slight and focal nuclear pleomorphism can be seen. Colloid is absent. Parathyroid adenomas are often mistaken for follicular lesions of the thyroid. Hypercalcemia, which is usually present in patients with parathyroid adenomas, is a clue to the diagnosis. Immunocytochemistry for thyroglobulin, which is positive in thyroid lesions, can be helpful.