Abstract Background Fine-needle aspiration cytology (FNAC) is useful for selecting patients with thyroid nodules for thyroidectomy. Its value in patients who have been exposed to low-dose therapeutic radiation is questionable because these patients have an increased risk of multifocal benign and malignant tumours, and thyroid cancer is common in such patients. Methods Between 1960 and 1999, 171 patients with one or more thyroid nodules who had a history of exposure to radiation underwent operation; 49 of these patients had preoperative FNAC. The cytology results in these 49 patients were compared with those of an age- and sex-matched control group of patients with thyroid nodules who did not have a history of radiation exposure. Results Of those who had been exposed to radiation, six of 20 patients with ‘benign’ cytology by FNAC and six of 16 patients with ‘suspicious’ cytology had thyroid cancer. All 13 specimens considered to be malignant on FNAC were indeed malignant. There was a higher rate of false-negative cytological examinations among patients with a history of irradiation that in those without. Conclusion FNAC of thyroid nodules in patients with a history of irradiation is not as accurate as that in non-irradiated patients, primarily because of coexisting occult thyroid cancers.