Unilateral vertebral artery (VA) injury is thought to not result in serious complications. The dominant-side VA should be preserved, although the importance of the nondominant-side VA has not been discussed. The injury of VA terminating posterior inferior cerebellar artery (PICA-VA) may result in cerebellar infarction. The characteristics of PICA-VA were evaluated. In study 1, results of head and neck magnetic resonance angiography were reviewed for 358 consecutive cases. VA diameter was measured at the V2 segment. Relationships between frequency of PICA-VA and asymmetry and diameter of the VA were analyzed. In study 2, results of magnetic resonance angiography were measured for 62 consecutive cases aged ≤39 years. Frequency of PICA-VA was compared between this young age group and 324 of the 358 cases aged ≥50 years. Mean age for the total cohort was 67.8 ± 13.8 years (range, 10–94 years). PICA-VA was identified in 44 cases (12.3%). Mean diameter of all VAs was 3.2 ± 0.76 mm. Mean diameter of PICA-VA was 2.0 ± 0.55 mm, significantly smaller than the nondominant side in Confluence (+) (2.8 ± 0.59 mm; P < 0.001). Among the 56 VAs <2.0 mm, 26 (46.4%) were PICA-VA. PICA-VA was seen in 1 of the 62 cases aged ≤39 years (1.6%), and in 43 of the 324 cases aged ≥50 years (13.3%), showing a significantly lower frequency in the younger population (P < 0.001). Whether PICA-VA injury causes complications is not obvious. However, PICA-VA should also be preserved considering that potential risks exist. If the VA is small or shows a large difference in diameter between sides, special care should be taken during cervical spine surgery.