To overcome the difficulties arising in the management of cold nodules of the thyroid--many are unnecessarily resected because of the risk of malignancy--fine needle aspiration cytology was used in the assessment of thyroid lesions in 113 patients. Aspirates were categorised into three groups as follows: group (i), consistent with simple goitre or cyst; group (ii), suspicious of underlying cellular lesion or tumour; group (iii), malignant. Resections for simple goitre were reduced from eight of 14 (40%) to two of 42 (3%) over three years, and the yield of neoplastic lesions coming to surgery as a result of aspiration increased from two of 12 (16%) to nine of 14 (69%) over the same period. It is concluded that fine needle aspiration cytology is an effective means of discriminating between simple and neoplastic thyroid lesions. This permits more appropriate patient management and a beneficial saving of resections for simple goitre. False negative diagnoses (two cases) in our series are of more concern than false positive results, but can be minimised by careful attention to sampling and cytological detail.