AIMS: To analyse the benefits and limitations of fine needle aspiration in the cytological differentiation of parenchymatous nodular goitres from follicular tumours in an endemic area. METHODS: Cytological smears of fine needle aspirates from 31 parenchymatous nodular goitres were studied. A sample from the punctured nodules was fixed in formalin and stained with haematoxylin and eosin for histological analysis. RESULTS: All nodules occurred in a multinodular gland, were well circumscribed, did not compress surrounding thyroid tissue, and for the most part, were unencapsulated. Two cases showed cytological features of nodular goitre, two of colloid cysts; the remaining 27 were cytologically indistinguishable from follicular lesions. CONCLUSIONS: Most of the parenchymatous nodules studied had features suggestive of follicular lesions or neoplasia, but surgical treatment should only be considered after hormone treatment has proved unsuccessful, and when they are not suspected as malignant clinically. Fine needle aspiration is useful as a diagnostic and screening aid, but the results should be interpreted with caution to prevent unnecessary surgery.