In childhood, a significant proportion of giant aneurysms usually occur at the vertebrobasilary system. Nonetheless, giant totally thrombosed aneurysm which only involves the vertebral portion of the vertebrobasilary system is very rare. Up to this time, in childhood, a few giant aneurysm originating from vertebral artery have been reported, and to our knowledge only one case was reported to be totally thrombosed. The enlargement tendency of totally thrombosed aneurysms and management of these cases are still controversial. Thus, diagnosis and follow-up of cases where a radical approach could not be performed require a multi-modality radiologic approach. In this study, we reported a case of angiographically occult giant thrombosed vertebral artery aneurysm, which is extremely rare, and discussed the importance of CT and MRI in evaluation of these patients before surgical treatment. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.