We analyzed early aneurysmal rebleeding in 150 consecutive patients who suffered an aneurysmal subarachnoid hemorrhage (SAH) and who were admitted within 6 hours of the initial SAH. Of these patients, 33 patients rebled. The first rebleed occurred within 24 hours in 29 patients, among whom 23 cases rebled within 6 hours. The rebleeding rate within 6 hours after the initial SAH was not related to age or sex of the patient; blood pressure on admission; size, shape, or site of aneurysm; or presence or absence of intracerebral hematoma or intraventricular hemorrhage on computed tomography (CT) scan. The patients' clinical condition and SAH on CT scan were graded I-V. Evaluation of rebleeding of those patients with grade V was difficult. In examining the rebleeding rate in grades I-IV, the higher the grade, the greater the rebleeding. Rebleeding developed during angiography conducted within 6 hours from the initial SAH in four cases. This is approximately twofold higher than the rebleeding rate within 6 hours for the total series. It is concluded that rebleeding in the acute stage is predominant within 6 hours from the initial SAH and that this rebleeding rate is higher the more severe the initial SAH is.