OBJECTIVE: The purpose of this study was to compare intensive insulin therapy and conventional therapy in terms of ventilator days, neurosurgical intensive care unit (NSICU) stay, Glasgow Outcome Scale (GOS), and complications for patients with a severe traumatic brain injury (TBI) who underwent decompressive craniectomy. METHODS: Patients who had a TBI and a Glasgow Coma Scale (GCS) score < or =8, and who had been treated with a unilateral or bilateral decompressive craniectomy were enrolled. Twenty-three patients were treated with intensive insulin therapy targeting 80-120 mg/dL of blood glucose level. For comparison, 17 patients with conventional insulin therapy (<200 mg/dL) were extracted from the historical data. RESULTS: There was no statistically significant difference in terms of sex, age, GCS at admission, diagnosis of TBI, and history of diabetes. There was no statistically significant difference between the conventional and intensive groups with respect to total days of mechanical ventilation, NSICU days, GOS, and pneumonia. Hypoglycemic episodes developed more frequently in the intensive insulin therapy group than in the conventional therapy group. CONCLUSION: Intensive insulin therapy with our protocol cannot be recommended over conventional therapy in patients with severe TBI.