Thirty consecutive patients with aneurysmal subarachnoid hemorrhage (SAH), 20 patients with ischemic stroke, and 100 controls were extensively interviewed about previous episodes of sudden headache, according to a standard pro forma. Thirteen patients with SAH (43%) had a history of a forewarning headache, compared with only one of the patients with ischemic stroke and none of the controls. The interval from the warning headache to the admission rupture was between one week and two months in all patients but one with SAH. Only half of the 13 patients with a warning headache consulted their physician. The outcome was slightly worse in patients with a warning headache, but the differences did not reach statistical significance. These data emphasize the frequent occurrence of warning headaches in SAH. Measures to increase the recognition of sudden headaches should be considered.