A rare case of ruptured aneurysm originating from the vertebral artery, and presenting an isolated clot in the fourth ventricle is reported. The patient underwent surgery via a right lateral suboccipital craniectomy on the third day. As the aneurysm was huge and partially thrombosed, trapping was performed and completed successfully. If isolated intraventricular hematoma was found without obvious parenchymal hemorrhage or subarachnoid clot, the diagnosis of vertebral artery aneurysm should be considered as a possibility in addition to posterior inferior cerebellar artery aneurysm. Complete vertebral angiography is indispensable for the recognition of this condition.