A case of recanalization of totally thrombosed giant aneurysm is reported. The authors describe a 18 year-old female who developed headache, vomiting. and intermittent diplopia with left side ptosis. The brain CT scan and MRI revealed a totally thrombosed giant aneurysm with acute and subacute hemorrhage, located anterior to the, left suprasellar cistern. Angiographic finding was non-visualization of the left posterior cerebral artery distal to the P2 segment, and the neck of the aneurysm was not identified. Follow-up angiography. taken one month later showed partial. recanalization of the thrombosed aneurysm. A probable mechanism of growth, thrombosis, and recanalization, of the giant aneurysms are-discussed.