A 75-year-old man with nodular goitre (for the preceding 2 years treated with 75 micrograms/dl L-thyroxine) complained of pain over the left hip: on auscultation an arterial flow murmur was audible over the hip. The radiograph demonstrated extensive osteolysis in the flat part of the ilium. Search for the primary tumour, including two pelvic angiographs, was unsuccessful. Examination of a biopsy from the right ilium revealed a metastasis from a highly differentiated follicular thyroid carcinoma, which could not be demonstrated scintigraphically because of a reduced 99mTc-pertechnetate and 123I-iodine uptake, the result of the L-thyroxine administration. A thyrotoxic crisis occurred 2 days after the second angiography (free thyroxine 3.17 ng/dl, triiodothyronine 219 ng/dl, thyroglobulin > 250 ng/ml). Treatment with thiamazole (40 mg/d) and perchlorate (1 g/d) reduced the concentration of peripheral thyroid hormone, but the patient's general condition improved only slowly. As a result, radioiodine treatment could not be started until 9 months later. He died a further 9 months later from septicaemia originating from the metastasis.