Hyperosmolar hyperglycaemic state (HHS) is a medical emergency which needs immediate medical intervention. A 37-year-old Chinese woman with a history of hypertension attended the Emergency Department. She had a two-day history of involuntary movement, i.e. chorea of the upper limbs, preceded by a one-week history of upper respiratory tract infection. She also had polyuria and polydipsia, although she was never diagnosed as diabetic. The main aim of reporting the present case was to highlight the importance of biochemical investigations involved in the diagnosis of involuntary movements.