The outcome of severe acute subdural hematoma is unfavorable. In particular, patients with levels of consciousness of Glasgow Coma Scale(GCS)3 or 4 tend to be refractory to treatment. Decompressive craniotomy should be promptly performed to remove hematoma. However, if an operating room is not immediately available, emergency burr hole surgery is sometimes performed in the emergency room(primary care room)prior to craniotomy. A previous study has reported that the interval from injury to surgery influences the outcome of severe acute subdural hematoma. Therefore, emergency decompression is important to effectively treat patients with severe acute subdural hematoma. We present the cases of two patients with acute subdural hematomas. In both cases, emergency decompressive craniotomy(hematoma removal after craniotomy and external decompression)was performed in the emergency room of the Emergency and Critical Care Center. In both cases, the surgery was followed by favorable outcomes. Case 1 was a 36-year-old female. The patient's level of consciousness upon arrival was GCS 3. The interval from injury to diagnosis on the basis of CT findings was 75 minutes. Surgery began 20 minutes after diagnosis. Case 2 was a 25-year-old male. The second patient's level of consciousness upon arrival was GCS 4. The interval from injury to diagnosis on the basis of CT findings was 60 minutes. Surgery was begun 40 minutes after diagnosis. In both patients, we observed anisocoria and the loss of the light reflex. However, the postoperative course was favorable, and both patients were discharged. In summary, to treat severe acute subdural hematomas, early emergency decompressive craniotomy is optimal. Emergency decompressive surgery in the emergency room is independent of operating room or staff. Therefore, emergency decompressive craniotomy may improve the outcome of patients with severe acute subdural hematomas.