The morphological features associated with cerebral arteriovenous malformations have been under increasing scrutiny since the advent of high-definition and superselective angiography; certain features may be associated with an increased risk of rupture. In the systemic circulation, the presence of a false aneurysm after the rupture of a vessel has been described; however, no similar phenomenon has been reported in the cerebral circulation. In this case report, we describe a false aneurysm in a young man who had an arteriovenous malformation that hemorrhaged in the posterior fossa. Computed tomography and magnetic resonance imaging revealed a posterior fossa hematoma in the lower brain stem and cerebellum. Angiography indicated that the arteriovenous malformation was fed primarily by the left posterior inferior cerebellar artery. The mass effect of the hematoma was visible as a hypodense region. In the middle of the hematoma, on the distal portion of the posterior inferior cerebellar artery, was a dilatation, measuring 4 x 5 mm, with a stagnation of the contrast medium that was pathologically consistent with a false aneurysm. The patient with a false aneurysm, such as the man we describe, runs a significant risk of hemorrhage at the time of resection of the arteriovenous malformation, with additional implications for endovascular treatment. The volume of embolic injections of the involved vessel should be limited to avoid raising the intra-arterial pressure, and the choice of embolic material must be tailored individually. Recognizing the presence of false aneurysm is important in the choice and timing of therapy.