Newly formed aneurysms developing from a cerebral vessel which had appeared to be normal in a previous angiographic study are very rare. Four cases of angiographically documented newly developed saccular aneurysms are described in this report. In all four patients, the new aneurysms were symptomatic, causing subarachnoid hemorrhage (SAH). Repeat angiography, performed after the second SAH, revealed new aneurysms that were not demonstrated on initial angiograms after the first SAH. They were clipped with good postoperative course. Our observations and literature data suggest that some patients with SAH need further neuroradiological followup. The presence of the risk factors and age of the patient should be taken into consideration.