A 27-year-old man, who had type 1 diabetes, presented with agitation, confusion, vomiting and faecal incontinence. There was an abscess on his right upper arm at an insulin injection site (temperature 38.5°C, pulse 140 per minute, and blood pressure 125/85 mmHg). Investigations included neutrophil count 13.6 ×10⁹/litre, glucose 26 mmol/litre, pH 7.4, free thyroxine (T₄)>77 pmol/litre (normal range (NR) 9–22.7), thyroid-stimulating hormone (TSH) <0.01 mu/litre (NR 0.35–5). After sedation with haloperidol 15 mg intramuscularly, he was rehydrated with physiological saline and treated with intravenous (IV) cefotaxime 3 g three times daily, IV dexamethazone 2 mg twice daily, IV methimazole 15 mg two doses 8 hours apart (Favistan injection solution, Temmler Pharma, Marburg, Germany), labetolol 120 mg (infused over 1 hour twice daily), and an insulin infusion using up to 4 u/hour. After 24 hours there was a marked clinical improvement with resolution of his agitation and confusion and his pulse rate was normal (T₄ 22 pmol/litre, TSH <0.05 mU/litre after 72 hours). He was discharged on carbimazole 60 mg daily and propranolol 20 mg four times daily, and had radio-iodine treatment (339 MBq) 6 months later. He is well on thyroxine 50 μg daily 2 years later.