Posterior inferior cerebellar artery (PICA) variations are well recognized; however, their mechanisms have not been well understood. Primitive lateral basilovertebral anastomosis (PLBA) was described in 1948 by Padget and is one of the embryological transient longitudinal channels in the hindbrain. This study reports a PICA aneurysm associated with PLBA. A 48-year-old man presented with subarachnoid hemorrhage. Cerebral angiography showed a 3.6-mm fusiform aneurysm with a bleb of the left PICA just at the origin of the PICA from the vertebral artery. Furthermore, a direct anterior inferior cerebellar artery (AICA)-PICA anastomosis parallel to the basilar artery was revealed. This direct anastomosis between the AICA and PICA is explained by the partial persistence of PLBA. Variations in the three cerebellar arteries and vertebrobasilar junction can be caused by persistence of PLBA.