The authors report a case of a posterior inferior cerebellar artery origin aneurysm causing brainstem compression and swallowing difficulty. The patient had an ipsilateral microvascular decompression of cranial nerve VII for hemifacial spasm 27 years prior to the discovery of the aneurysm. The aneurysm was successfully treated endovascularly. A discussion of possible etiologies of the aneurysm's formation is presented.