Two cases involving a ruptured aneurysm in a choroidal branch of the posterior inferior cerebellar artery are reported here. Case 1: A 61-year-old woman was admitted after an episode of severe headache with persistent vomiting. A CT revealed an intraventricular hemorrhage within the fourth ventricle. An angiography showed an aneurysmal shadow in the choroidal artery branching from the telovelotonsillar segment of the distal posterior inferior cerebellar artery (PICA). The operation disclosed a fusiform aneurysm in the choroidal artery which was successfully trapped using Yasargil's mini-clips. The postoperative course was uneventful and the patient was discharged without any neurological deficit. Case 2: A 64-year-old woman became unresponsive after complaining of a severe headache. On admission, she was semicomatose with positive bilateral Babinski's sign. A CT scan showed that the fourth and third ventricles were packed and dilated by a massive hematoma. An angiography demonstrated an aneurysmal shadow in a branch from the PICA with an occlusion of the right vertebral artery. Furthermore, the left vertebral artery was also occluded and the basilar artery was fed by collateral circulation. The patient underwent an operation immediately. The fusiform aneurysm was resected after ligation. Her postoperative course was satisfactory. She was able to go home without neurological deficit. There has been only one article about "pure" choroidal artery aneurysm, reported by Uranishi, et. al in 1994. They suggested that the pathogenesis of this lesion could be due to hemodynamic stress. Our two cases also present the same characteristics, in the shape of the aneurysms as well as in the anomalous structures in the posterior circulation. Our results offer further evidence concerning the pathogenesis of that type of lesion.