The value of fine needle aspiration (FNA) cytology in the diagnosis of ultrasonically suspected parathyroid gland enlargements was reviewed for a six-year series of cases. In 146 patients, 277 FNA biopsies under ultrasound guidance were performed on suspected enlarged parathyroid glands. Smears were routinely stained by the Pappenheim (May-Grünwald-Giemsa) method, and the Grimelius silver stain was used to demonstrate argyrophilic granules in the cytoplasm of parathyroid cells. Diagnostic material was obtained by FNA from 121 (83%) patients, whereas the aspirates were considered inadequate for cytologic diagnosis in 25 (17%) patients. For the 121 cases with adequate FNA samples, cytology diagnosed a parathyroid origin in 80 (55%) of the 146 total patients) and a thyroid origin in 41 (28%). The cytologic-histologic correlation available for 36 patients showed a cytologic sensitivity of 86%. Parathyroid lesions are frequently treated preoperatively as a disease of the thyroid; the results of this study suggest that cytomorphologic analysis of FNA samples can demonstrate the parathyroid origin of such samples, especially when a silver stain is used in addition to the routine stain.