Of 312 consecutive patients who were admitted to an emergency hospital because of subarachnoid hemorrhage (SAH), data on premonitory minor leaks were available on 303. Patients with an aneurysmal SAH had significantly (P less than 0.05) more frequently (100 of 273, or 37%) a history of symptoms consistent with a previous minor leak than those with a hemorrhage of unknown etiology (4 of 30, or 13%). Aneurysmal SAH was associated with a poorer prognosis, more frequent occurrence of repeated bleeding and cerebral ischemia compared with SAH of unknown etiology, even in the good grade patients. The possible occurrence of a minor leak in poor grade patients may be even more frequent because the history obtained from family members was quite often uncertain. The outcome did not differ according to the evidence of previous minor leaks, but those who were admitted before a major rupture had a good outcome. The median time between a minor leak and major rupture was 14 days (range, 1 day to 4 mo). The correct diagnosis of a minor leak is important because early diagnosis and management can improve the overall outcome of this disastrous disease.