In the present report, we describe a case of dissecting aneurysm of the vertebral artery (VA) involving the posterior inferior cerebellar artery (PICA). A 64-year-old woman presented with vomiting and disturbed consciousness. Computed tomography (CT) imaging revealed a subarachnoid hemorrhage with intraventricular hemorrhage. Three-dimensional computed tomography angiography revealed a dissecting aneurysm of the left VA involving the PICA, located at the proximal end of its dissection. The aneurysm was successfully treated by trapping and diagonal proximal occlusion, which enabled the preservation of the PICA.