195 patients affected by a cystic thyroid lesion were studied by a Fine Needle Aspiration biopsy (FNAb). 42 patients were operated on account of clinical data, compressive phenomena or cytologic results suggesting a neoplasia. Out of the operated patients, 3 were affected by a carcinoma in the cystic lesion (one "pure" cystic nodule and two "mixed" ones), while three more patients with multinodular goiters showed a carcinomatous lesion in a nodule different from the cystic one. Macroscopic characteristics of the aspirated fluid (quantity and quality) didn't affect the cytologic diagnosis. Cytology was useful in the preoperative diagnosis of benign thyroid nodules (only two false positives out of 42 patients) and was diagnostic in all the three patients affected by a carcinoma in the cystic nodule.