An 85-year-old man with a history of diabetes was admitted with acute onset hemichorea. Laboratory findings confirmed poorly controlled diabetes. A brain computed tomography (CTC) revealed contralateral striatal hyperdensity. The findings were compatible with hyperglycaemia-induced hemichorea, and antidiabetic and symptomatic treatment was initiated. The symptoms remitted completely after six days, and a follow-up CTC showed partial resolution of the striatal changes. This case illustrates the importance of considering if hyperglycaemia is the cause of hemichorea, as early diagnosis and treatment yield an excellent prognosis.