Bow hunter's syndrome (BHS) is most commonly caused by compression of the 
vertebral artery (VA). It has not been known to occur due to an extracranially 
originated posterior inferior cerebellar artery (PICA), the first case of which 
we present herein. A 71-year-old man presented with reproducible dizziness on 
leftward head rotation, indicative of BHS. On radiographic examination, the 
bilateral VAs merged into the basilar artery, and the left VA was predominant. 
The right PICA originated extracranially from the right VA at the atlas-axis 
level and ran vertically into the spinal canal. During the head rotation that 
induced dizziness, the right PICA was occluded, and a VA stenosis was revealed. 
Occlusion of the PICA was considered to be the primary cause of the dizziness. 
The patient underwent surgery to decompress the right PICA and VA via a 
posterior cervical approach. Following surgery, the patient's dizziness 
disappeared, and the stenotic change at the right VA and PICA improved. The PICA 
could be a causative artery for BHS when it originates extracranially at the 
atlas-axis level, and posterior decompression is an effective way to treat it.