Object. The purpose of this study was to report the potential proneness of a fetal-type posterior cerebral artery (PCA) to develop vascular insufficiency in parent vessel occlusion of distal PCA aneurysms. Methods. Between January 2005 and January 2011, 19 patients (9 females and 10 males) with 20 distal PCA aneurysms (16 dissecting and 4 saccular) were treated with endovascular parent vessel occlusion. The ages of the patients ranged from 5 to 71 years, with a mean age of 40.2 years. Of the 20 aneurysms, 4 were ruptured and 16 were unruptured. One of the unruptured aneurysms was additional to another ruptured aneurysm, and 15 were incidentally discovered. Five aneurysms were smaller than 10 mm, and the other 15 were 10 mm or larger. Results. All aneurysms were successfully treated with simultaneous coil occlusion of the aneurysm and the parent PCA. One patient had hemianopia at the initial presentation, and 2 patients had new persistent hemianopia due to insufficient leptomeningeal collateral circulation; in 16 patients with an intact visual field, no hemianopia developed because there was sufficient leptomeningeal collateral circulation. A fetal-type PCA was involved in all 3 patients with hemianopia, which was initially presented or caused by parent vessel occlusion. However, in the patients without hemianopia, an adult-type PCA was involved in all cases. Conclusions. Endovascular treatment via coil occlusion of the aneurysm as well as the parent artery can be used to cure distal PCA aneurysms. A fetal-type PCA could be an important predictive factor for vascular insufficiency in parent vessel occlusion treatment. (http://thejns.org/doi/abs/10.3171/2012.4.JNS111788)