In a retrospective study volumes of 42 extradural and 102 subdural traumatic hematomas were evaluated. Results were related with the time interval between injury and initial CT scan, outcome, coma grade and subject age. Mean volumes were found to increase with time after the injury. In the first hour volumes of 8 intracranial hematomas were hardly space consuming, while they became clearly space consuming in the second and in later hours after the injury. It was therefore concluded that it should not take longer than one hour until a CT scan be performed when an intracranial post-traumatic hematoma is suspected in the comatose patient.