PURPOSE: Spontaneous subarachnoid hemorrhage(S-SAH) is a relatively rare disease with good clinical course and prognosis. The purpose of this study is to evaluate the cisternal blood distribution on CT in patient with S-SAH. MATERIALS AND METHODS: Out of 406 patients with subarachnoid hemorrhage on brain CT scan, 11 patients confirmed to be S-SAH by angiography and clinical follow-up were examined. We analysed the CT findings of these 11 cases retrospectively. RESULTS: Five patients had only perimesencephalic distribution of hemorrhage:the prepontine, the interped- uncular, and the suprasellar cisterns were involved in 4 cases each, the basal sylvian cistern in 3 cases, and the ambient cistern in 2 cases. The quadrigeminal and a portion of the lateral sylvians were also involved in 1 case each. Six patients revealed cisternal hemorrhage extending beyond the perimesencephalic cistern into the ventricles, cortical sulci, and lateral sylvian fissure. Intraventricular hemorrhage was noted in 3 cases of these 6 patients. CONCLUSION: Our study suggests that uncomplicated clinical course and normal anglographic finding are more important than CT distribution of cisternal hemorrhage in diagnosing S-SAH.