The clinical significance of traumatic subarachnoid hemorrhage (TSAH) was studied in 20 head-injured patients. They were classified into mild (9) and severe (11) groups by their initial Glasgow Coma Scale (GCS) scores. TSAH detected by computed tomography was localized in the Sylvian fissure in four of the nine mild group patients, but was also found in other basal subarachnoid cisterns in the other five. Except for one patient who developed delayed vasospasm and communicating hydrocephalus, all had favorable outcomes in this group. Massive TSAH was noted in the basal subarachnoid cisterns in 10 severe group patients and only one had a good outcome. Delayed intracerebral hematoma in the frontal or temporal lobe in the vicinity of the Sylvian fissure was found in two mild and two severe group patients with TSAH in the Sylvian fissures. Traumatic parenchymal lesions in the brainstem were minimal in one of the two autopsied patients and no evidence of diffuse axonal injury was found in both cases. Thus, TSAH in the Sylvian fissure is suggestive of focal brain contusion around the fissures. Massive TSAH in the basal subarachnoid cisterns is not necessarily associated with severe parenchymal injury of the brainstem.