Subdural hematoma is divided roughly into two types acute and chronic. The two show an entirely different mode of illness. The authors have encountered 4 cases of subacute subdural hematoma in which characteristics of both types coexisted. These cases are characterized by the following. 1) The disease develops in the elderly persons with a history of trauma unknown or after minor head injury. 2) There is a relatively long period of clear consciousness and they visit a hospital when they are in the subacute stage, 3) They have a history of drinking alcohol heavily as a habit and there is a high risk of hypertension and diabetes. 4) Brain CT findings sometimes reveals mixed density hematoma. 5) Hemorrhage from the cortical artery is occasionally noted as the operative findings. Hematoma membrane is absent. 6) The outcome is generally poor because of systemic complications. As described above subacute subdural hematoma was similar to chronic subdural hematoma in the clinical course and CT findings. But operative findings of this disease indicated acute subdural hematoma. Repeated minor hemorrhage, related to coagulation disorder and brain atrophy would be important as the mechanism of subacute subdural hematoma. The effectiveness of perforation craniotomy as radical operation was low and removal of hematoma by major craniotomy was needed. The concept of subacute subdural hematoma is considered important in deciding on a therapeutic policy.