Sixty-four patients who were operated on within 4 days after acute subarachnoid hemorrhage are included in this study. All patients underwent preoperative computed tomographic (CT) scanning, and the amount and distribution of subarachnoid blood clot were noted. Operation was carried out by the frontobasal lateral approach, and the subarachnoid clot was removed by microsurgical suction-irrigation after clipping of the aneurysm. Immediate postoperative CT scanning was performed to evaluate the completeness of the subarachnoid blood clot removal. The presence or absence of postoperative vasospasm was determined with angiography performed between the 7th and 10th postoperative days. All patients were, of course, also evaluated for evidence of neurological deterioration. Approximately two-thirds of the patients in this series showed high density subarachnoid blood clot on the preoperative CT scan. The postoperative CT scans showed that it was possible to remove the majority of the blood clot except that located in the frontal interhemispheric fissure, the posterior part of the insular cistern on the approached side, and all of the insular cistern on the contralateral side. There was no spasm or only mild spasm in any site where the blood clot had been successfully removed. Delayed neurological deficits occurred only in those cases in which subarachnoid blood clot remained in the cisterns. These results suggest that it is possible to prevent intracranial arterial spasm and associated neurological deterioration by early operation and removal of clotted blood from the subarachnoid space.