The object of this study was to determine the relationship between plasma taurine and subarachnoid hemorrhage (SAH) outcome. Forty patients with SAH and mild neurological deficits were included in this prospective, blinded cohort study. Plasma taurine levels were measured using high-performance liquid chromatography on admission and were correlated with patient outcomes at discharge. Twenty-five percent of the patients ultimately had a poor outcome. Plasma taurine concentrations at admission were increased (2-fold) in SAH patients with a favorable outcome and were further increased (6-fold) in those who had a poor outcome. Increased taurine levels identified patients who would be discharged with a poor outcome, with sensitivity and specificity values of approximately 80% and 100%, respectively, and positive and negative predictive values of approximately 90%. Delayed cerebral vasospasm showed an OR of 27.9 (95% CI 1.090-714.9) for a poor outcome, whereas an increased taurine concentration had an OR of 105 for a poor outcome (95% CI 8.3-1328.0, p < 0.001). Increased plasma taurine concentrations on admission predict a poor outcome in SAH.