A 65-year-old woman with type 2 diabetes mellitus was found in an unresponsive state and she was admitted to our hospital. She was comatose on arrival. The bedside blood glucose level on admission was 15 mg/dl (normal range, 55-110 mg/dl). After emergency infusion with 50% dextrose, the blood glucose level rapidly normalized to 98 mg/dl, but there was no clinical improvement of her consciousness. Three days after admission, diffusion-weighted magnetic resonance imaging of the brain revealed bilateral temporal, occipital and frontal lobes lesions with high signal intensity. The patient's neurological condition did not change over the next 15 days. She died of pneumonia on the 30th day of hospitalization. DWI may be useful for detecting and making the differential diagnosis of hypoglycemic coma. Further, marked differences in the neuroimaging patterns of patients in a hypoglycemic coma are valuable prognostic predictors. We report here on a case of hypoglycemic coma with a poor outcome.