Introduction : Choreic ballism is a rare neurologic complication of metabolic origin in non ketotic hyperglycemia although the etiologic mechanism is still unclear. Sometimes, It was reported in poorly controlled old female type 2 diabetes mellitus. We experienced repeated attacks of left upper arm hemichoreic movement following to uncontrolled hyperglycemia in type 2 diabetes mellitus patient. Clinical case: A 68-year-old woman with 11-year history of type 2 diabetes mellitus who was admitted to our hospital for recurred attack of hemichoreic movement in the left upper limb of the body. On admission day, her glycosylated hemoglobin was 13% (N:4-6%). Her calculated serum osmolarity peaked at 310 mOsm/kg (N: 275- 295mOsm/kg), and the serum glucose level reached 475 mg/dl (N:80-140mg/dl). The initial serum sodium level was 135 mmo/L (N:135-145 mmol/L), which normalized to 142 mmol/L over 1 day. The physical examination revealed left hemichorea with a ballistic component without no focal neurologic fi nding. Unenhanced computed tomography of the brain was negative. At magnetic resonance imaging, the right putamen showed high signal intensity on T1-weighted images. During the hospitalization, an adequate diet therapy and insulin therapy resulted in progressive normalization of blood glucose values and an improvement of dyskinesia. According to medical records, she was admitted previously due to hemichoreic movement attack 4 times whenever her blood glucose was uncontrolled. Conclusions: The pathogenesis of chorea seems to be related to both vascular and neuro-metabolic alterations in the basal nucleus due to inadequate glycemic control continuously in type 2 diabetes mellitus. But this rare complication is a pathological entity to be considered benign, since it is generally transient and reversible. So early recognition and differentiation from other causes of this manifestation in uncontrolled type 2 diabetes mellitus is important.