Most trauma deaths are related to traumatic brain injury (TBI). Although the management of patients has improved, mortality remains unacceptably high, and half of survivors of moderate and severe TBI are left with major functional impairment. Current management guidelines are based on limited evidence and practice is highly variable. Most acutely ill patients with TBI will develop anemia, which may decrease oxygen delivery to a fragile brain. While clinical practice is moving towards transfusing at low hemoglobin (Hb) levels, experts have expressed concerns regarding restrictive strategies, which may adversely affect clinical outcomes in TBI. Our primary objective is to evaluate the effect of red blood cell (RBC) transfusion thresholds on neurological functional outcome. We hypothesize that a liberal transfusion strategy improves outcomes compared to a restrictive strategy.