Percutaneous embolization using a detachable balloon in six cases of vertebral fusiform aneurysm is reported. Location of these aneurysms were as follows; 5 aneurysms in the distal vertebral artery (2 proximal to the posterior inferior cerebellar artery; PICA, 2 distal to the PICA and 1 where the PICA was undetectable), and one aneurysm in the extracranial vertebral artery. Three cases suffered from subarachnoid hemorrhage (dissecting aneurysms) and other cases showed lower cranial nerve palsy (giant aneurysm) or posterior fossa ischemia. Most of the cases were treated immediately after conventional diagnostic angiography, especially those cases with subarachnoid hemorrhage (within 4 days after the last attack). Under local anesthesia, a catheter was positioned in the affected vertebral artery either trans-femorally or trans-axillary. The detachable balloon was placed proximal to the aneurysm and test occlusion was performed for 15-20 minutes (the tolerance test or balloon Matas' test). After it was confirmed that there had been no neurological deterioration, the vertebral artery was permanently occluded by detachment of the balloon. The procedure was successful in all cases. Thrombosis of aneurysms was confirmed either by follow-up angiography or by autopsy. However, two cases who were grade V (Hunt & Kosnik) at admission died of severe vasospasm. PICA was preserved through either ipsilateral or contralateral collaterals. Detachable balloon occlusion of the vertebral artery for fusiform aneurysm is thought to be less invasive, more indicative and a safer procedure compared to conventional surgical proximal occlusion therapy.