Postoperative intracranial infections, although found in only a minority of surgical cases, remain a recognized potential complication following elective craniotomy. In the treatment of intracranial aneurysms, specifically, reports of significant postoperative infections are rare. Significant postoperative infections are usually observed in association with foreign bodies, such as aneurysm clips, endovascular coils, or materials used for aneurysm wrapping. The authors present a case in which a patient underwent craniotomy for surgical clip ligation of a giant ophthalmic artery aneurysm without resection of the aneurysm mass; the patient then presented again approximately 4 months later with a first-time seizure. Following a second craniotomy for resection of the aneurysm mass, the aneurysm contents were noted on pathological examination to contain gram-positive rods, and the aneurysm wall was noted to contain inflammatory cells. Although cultures were not obtained, Propionibacterium acnes was detected using polymerase chain reaction. To the best of the authors' knowledge, this case represents the second reported case of an intraaneurysmal abscess and the first reported instance of a presumed secondary infection of a giant intracranial aneurysm remnant following surgical clip ligation.