Computed tomography of 31 patients with spontaneous subarachnoid hemorrhage (SAH) but negative angiography was evaluated to find out whether the pattern of SAH as seen in CT offers indications for a possible reexamination with angiography. Based on the distribution and the amount of SAH, classification into three groups was possible: (a) 18 cases, normal CT (but blood in the CSF, gained by lumbar puncture) or SAH in the basal cisterns only; repeat angiography was negative in all these cases; (b) nine cases, SAH in the basal cisterns as well as in one or both Sylvian fissures; in addition, small amounts of blood in the interhemispheric fissure and/or in the sulci; repeat angiography revealed an aneurysm in one of these cases; (c) four cases, large quantities of blood in all subarachnoid spaces; in all but one of these cases a vascular lesion was visualized with repeat angiography or verified at autopsy. In conclusion, repeat angiography is mandatory in cases with SAH patterns that can be classified into group b or c, whereas it can be omitted in patients with small amounts of blood confined to the basal cisterns.