The aneurysm nature and configuration in a giant aneurysm of the PCA is important and careful angiographic examination is needed. We present a case of dissecting aneurysm of the posterior cerebral artery masquerading as saccular giant aneurysm. A 17-year-old man presented with subarachnoid haemorrhage. Cerebral angiograms on admission showed a giant saccular aneurysm with wide neck at P1-P2 junction. The patient underwent endovascular coils embolization and extraventricular drainage of cerebrospinal fluid successfully. However, the patient was aggravated neurologically and got the rebleeding on postembolization 8 days. Repeat cerebral angiograms revealed dilated P1 segment with aneurysmal change of P2 segment. We report the angiographic feature and unusual clinical course and discuss the endovascular treatment of dissecting aneurysms.