Aneurysmal subarachnoid hemorrhage (SAH) is frequently complicated by delayed ischemic neurological deficit (DIND) due to cerebral vasospasm. Forty-five patients who had sustained an aneurysmal subarachnoid hemorrhage underwent HLA-typing. The HLA-typing was studied in order to assess its possibility of prediction to manifest symptoms of DIND. Significant increase of HLA-A31 and HLA-Aw33 was found in patients with SAH. In patients who showed DIND, HLA-Bw60 increased significantly when compared with controls from the same geographic area. Among the patients who did not develop DIND in spite of severe SAH, HLA-A24 decreased significantly, and HLA-31 and HLA-Aw33 showed a remarkable increase when compared with controls. These results suggest that HLA-A24 and HLA-Bw60 play a role as a predisposing factor of DIND resulting from vasospasm following aneurysmal SAH, and that HLA-A31 and HLA-Aw33 exert protective influence against DIND.