BACKGROUND The APOE-epsilon4 allele has been identified as a risk factor for Alzheimer's disease and unfavorable outcomes after brain injuries. The purpose of this study was to confirm that APOE allele polymorphism also represents a risk factor for unfavorable outcomes following aneurysmal subarachnoid hemorrhage (SAH). METHODS A total of 104 patients with aneurysmal SAH were studied. Computed tomography (CT) scan findings of SAH were assessed by Fisher's grade and clinical neurologic assessment was performed using the Hunt and Hess (H&H) grading system. Serum lipids were also analyzed. Outcomes at 3 months after SAH were determined using the Glasgow Outcome Scale. RESULTS The distributions of APOE genotypes and alleles of patients were matched with those of control subjects. That 5 of 18 patients with APOE-epsilon4 allele (28%) had an unfavorable outcome was significantly different from those without APOE-epsilon4 (8%, chi(2) p = 0.032; OR = 4.34, 95%C 1.20-15.75). However, the presence or absence Of epsilon2 or epsilon3 alleles had no significant difference. The relative hazard of APOE-epsilon4 for unfavorable outcome exited after adjustment for clinical assessment (OR = 6.95, 95%CI 1.2139.75). Total serum cholesterol, low-density lipoprotein and apolipoprotein B were elevated in patients with unfavorable rather than favorable outcomes. CONCLUSION Our findings confirmed that the patients with APOE-epsilon4 allele were predisposed to unfavorable outcomes after aneurysmal SAH even though an association between APOE and incidence of the SAH may not exist. The effect of APOE on neurobiology and lipoprotein metabolism seems to partially explain the difference in outcomes and deserves further study. (C) 2003 Elsevier Inc. All rights reserved.