During long term follow-up after successful treatment of ruptured intracranial aneurysms, a few patients develop newly formed (de novo) aneurysms, which account for 0.9-1.1% of all cerebral aneurysms. As for the etiology of de novo cerebral saccular aneurysms, hemodynamic stress is considered to be the most important factor. The woman whose case we present here had developed a ruptured anterior communicating aneurysm at the age of 52, and the aneurysm with its anterior projection was completely clipped. Eight years later, she suffered intraventricular hemorrhage. Angiogram showed a newly formed anterior communicating artery aneurysm, which projected to the side opposite the clip. Surgical exploration found the head of the clip had rotated and become trapped between optic nerves. We speculated the rotation of the clip used for the aneurysm at the first operation was one of the possible mechanisms, which caused a change in the direction of hemodynamics to the anterior communicating artery, leading to the development of de novo aneurysm. Every neurosurgeon should pay attention to the clip position until dural closure has been completed.