Background and purpose: The purpose of this study is to investigate the relationship between Rosenthal basal vein (BVR) type and diameter and perimesencephalic nonaneurysmal subarachnoid hemorrhage (P-SAH). Materials and methods: Aneurysmal subarachnoid hemorrhage (A-SAH), P-SAH, and control groups were evaluated, and BVRs were classified by type. BVR diameters in patients were measured. Results: There was a statistically significant difference of BVR drainage types between groups (P=002). BVR diameters of patients with normal drainage pattern in P-SAH group were significantly smaller than those in both other groups (P<.001). Conclusion: There is a relationship between P-SAH and BVR primitive drainage type. P-SAH risk increases in parallel with decreasing caliber of BVR in patients with normal drainage pattern. © 2014 Elsevier Inc.