In December, 2008, an 18-year-old woman, presented with weight loss, palpitations, dyspnoea, heat sensitivity, and excessive sweating. On examination, her pulse rate was 140 bpm and regular, and her blood pressure 130/60 mm Hg. Her weight was 48 kg and height 158 cm. She was anxious and hyperkinetic, with a thyroid stare and lid lag. She had a fi ne tremor of her hands. Her thyroid was diff usely enlarged (WHO goitre grading 2–3) and had an audible bruit. Thyroid hormone concentrations were high (free tri-iodothyronine 16·0 pmol/L, normal 3·1–7·4; free thyroxine 59·2 pmol/L, normal 10·3–21·9) and thyrotropin was suppressed (0·003 mIU/L, normal 0·45–4·5). Test for thyroid receptor antibody was strongly positive at 34 U/L (normal <1). A technetium scan revealed diff use thyromegaly with homogeneously intense uptake. 24 h thyroidal radioactive iodine uptake was 78%, and a diagnosis of Graves’ hyperthyroidism was made. Methimazole (10 mg three times daily) and propranolol (20 mg three times daily), were prescribed. After ten weeks, treatment with 16 mCi of radioactive iodine-131 was undertaken. Unexpectedly, 6 months later, a 3 cm fi rm nodule was palpable in the region of thyroid right lobe; the left lobe was barely palpable. Thyroid hormone concentrations were still high (free tri-iodothryronine 7·6 pmol/L; free thyroxine 21·9 pmol/L) and thyrotropin was low (0·02 mIU/L). Sonography showed a slightly enlarged thyroid with a solitary nodule in the right lobe. Scintigraphy showed that the nodule was hyperfunctioning (hot node) with no isotope uptake in the rest of