Peripheral aneurysms of the posterior inferior cerebellar artery (PICA) are rare. The authors report 15 cases of peripheral PICA aneurysms. Twelve of the aneurysms were discovered after their rupture and two were discovered after rupture of concomitant AVM, and one was detected incidentally. As to the location of aneurysms, more than half of the aneurysms arose at the telovelotonsillar segment. One patient had 2 aneurysms on the same peripheral PICA, which were not obvious on preoperative angiography because the ruptured one was partially thrombosed. Another rare case with aneurysm located at the internal auditory meatus is also reported. The findings of CT were characteristic, namely hemorrhage in the fourth ventricle without obvious hemorrhage in the basal cisterns, or only within the cerebellar vermian cistern. This phenomenon strongly suggested the possibility of rupture of peripheral PICA aneurysms. As to the surgical results, 10 patients (71%) of the 14 patients had a good recovery, and 1 patient (7%) with nonrupture aneurysm had a fair result due to pre-existing pontine hemorrhage. Three patients (21%) died. Rebleeding occurred in 3 patients, but cerebral vasospasm occurred in only 1 patient. Consequently, as peripheral PICA aneurysms are likely to be missed, and rebleeding is an unfavorable factor, one should try to demonstrate aneurysms with angiography, by using various methods such as subtraction or magnification.