In a recent study from the Mayo Clinic on the natural history of intact saccular intracranial aneurysms, none of the aneurysms smaller than 10 mm in diameter ruptured. It was concluded that these aneurysms carry a negligible risk for future hemorrhage and that surgery for their repair could not be recommended. These findings and recommendations have been the subject of much controversy. The authors report three patients with previously documented asymptomatic intact saccular intracranial aneurysms smaller than 5 mm in diameter that subsequently ruptured. In Case 1, a 70-year-old man bled from a 4-mm middle cerebral artery aneurysm that had been discovered incidentally 2 1/2 years previously during evaluation of cerebral ischemic symptoms. A 10-mm internal carotid artery aneurysm and a contralateral 4-mm middle cerebral artery aneurysm had not ruptured. Case 2 was that of a 66-year-old woman who bled from a 4-mm pericallosal aneurysm that had been present 9 1/2 years previously when she suffered subarachnoid hemorrhage (SAH) from a 7 x 9-mm posterior inferior cerebellar artery aneurysm. Although the pericallosal aneurysm had not enlarged in the intervening years, a daughter aneurysm had developed. The third patient was a 45-year-old woman who bled from a 4- to 5-mm posterior inferior cerebellar artery aneurysm that had measured approximately 2 mm on an angiogram obtained 4 years previously; at that time she had suffered SAH due to rupture of a 5 x 12-mm posterior communicating artery aneurysm. These cases show that small asymptomatic intact saccular intracranial aneurysms are not innocuous and that careful consideration must be given to their surgical repair and long-term follow-up study.