Background and PurposeWe sought to test the hypothesis that breathing 100% oxygen for the first 24 hours after an acute stroke would not reduce mortality, impairment, or disability.MethodsSubjects admitted to the Central Hospital of Akershus, Norway, with stroke onset <24 hours before admittance were allocated to 2 groups by a quasi-randomized design using birth numbers. All patients with acute stroke admitted to hospital within 24 hours after a stroke were included and enrolled. Patients were allocated to a group that received supplemental oxygen treatment (100% atmospheres, 3 L/min) for 24 hours (n=292) or to the control group, which did not receive additional oxygen. Main outcome measures were 1-year survival, neurological impairment (Scandinavian Stroke Scale), and disability (Barthel Index) 7 months after stroke.ResultsOne-year survival was 69% in the oxygen group and 73% in the control group (OR 0.82; 95% CI 0.57 to 1.19;P=0.30). Impairment scores and disability scores were comparable 7 months after stroke. Among patients with Scandinavian Stroke Scale (SSS) scores of ≥40, 82% in the oxygen group and 91% in the control group survived (OR 0.45; 95% CI 0.23 to 0.90;P=0.023). For patients with SSS scores of <40, 53% in the oxygen group and 48% in the control group survived (OR 1.26; 95% CI 0.76 to 2.09;P=0.54).ConclusionsSupplemental oxygen should not routinely be given to nonhypoxic stroke victims with minor or moderate strokes. Further research is needed to give conclusive advice concerning oxygen supplementation for patients with severe strokes.