A 24-year-old male Chinese student from southern China presented with sudden onset of generalized weakness. The evening before admission he had played football for 3 hours, and eaten a Chinese takeaway plus two hamburgers. He awoke in the early hours of the following morning unable to move his arms or legs. There was no history of any recurring illness and in particular there were no symptoms suggestive of hyperthyroidism. On examination the only abnormality was a profound symmetrical muscle weakness more marked proximally than distally (Medical Research Council (MRC) classification grade 1–2). Sensation to light touch and pinprick was normal. There were no signs of thyrotoxicosis. Laboratory investigations revealed the following (normal values in parentheses): serum potassium 1.2 mmol/litre (3.5–5.0); urinary potassium 14 mmol/litre (20–60); phosphate 0.18 mmol/litre (0.8–1.45); sodium, urea, and creatinine levels were normal. Electrocardiogram showed first degree atrioventricular block, prolonged QT interval and right axis deviation. He was given 120 mmol of intravenous potassium supplement over 12 hours. Over the next 24 hours his serum potassium returned to 4 mmol/litre, with complete resolution of the weakness. Subsequent investigations showed the following thyroid hormone measurements: thyroid-stimulating hormone (TSH) <0.08 mU/litre (0.5–6.0), triiodothyronine (T₃) 3.7 nmol/litre (1.0–2.5), free thyroxine (T₄) 53.7 pmol/litre (9.0–25.0), and thyroid peroxidase antibodies 124 IU/ml (0–75). He was HLA B46 and D9 positive. Ultrasonography of the thyroid gland revealed a mildly enlarged, heterogeneous thyroid with no discrete nodules and increased vascularity throughout. He was started on treatment with propranolol and carbimazole and returned home to China to seek further medical treatment.