[Natural history of unruptured cerebral aneurysms of the unoperated and observed cases].

Purpose: Natural history of unruptured cerebral aneurysms is still a matter of discussion. In this study, we investigated the prognosis of unruptured cerebral aneurysms of unoperated cases in a prospective design.

Methods: Between September, 1992 and December, 2001, we have encountered a 256 cases of unruptured cerebral aneurysms.