The cytologic findings in a fine needle aspirate of a functioning parathyroid carcinoma are presented. The smears were highly cellular. The most peculiar feature was the large number of dissociated cells scattered as free elements, with scanty or no cytoplasm and characterized by a marked variation in nuclear size. Several giant nuclei with multiple enlarged nucleoli were present. Clusters of atypical cells with moderate variation in nuclear size and chromatin content were mixed with groups of clear cells with abundant vacuolated cytoplasm and poorly outlined cellular borders. Clear cells were often seen palisading along fibrous vascular septa. The differential diagnosis is discussed.