The association of Graves' disease with thyroid nodules and thyroid carcinoma is rarely reported. The incidence seems to be increasing according to recent literature. The aim of this multicentre study was to review patients who had surgery for Graves' disease associated with thyroid nodules, and to evaluate the risk of thyroid carcinoma. A retrospective study was made of 557 consecutive patients who underwent operation for Graves' disease between 1991 and 1997 in five endocrine surgery departments. Each patient underwent clinical, biochemical, ultrasonographic and scintigraphic evaluation. None of the patients had had previous radioactive iodine therapy or external irradiation. Surgery consisted of either a subtotal or total thyroidectomy. Nodules were observed before operation in 140 patients (25.1 per cent). Thyroid carcinoma was diagnosed in 21 patients (15.0 per cent), always inside a nodule. The incidence of thyroid carcinoma associated with Graves' disease was 3.8 per cent (21 of 557 patients): 20 papillary and one follicular carcinoma. The carcinoma was multifocal in two patients. Tumour diameter ranged from 2 to 25 mm. A nodule was palpable in four patients. This multicentre study of patients having thyroidectomy for Graves' disease showed that 3.8 per cent had a carcinoma; the rate of carcinoma in cold nodules was 15.0 per cent. Surgery should be advised in any patient with Graves' disease and a thyroid nodule; the operation should be total thyroidectomy.