The initial hemoglobin (Hb) levels and vital signs of 1,000 patients treated with intravenous infusion in the admission area of Groote Schuur Hospital Trauma Unit were recorded. The mean Hb level of 860 patients with mild or no signs of shock was 12.7 g/dL. Lower mean Hb levels were noted in 91 moderately shocked patients (11.8 g/dL, p less than 0.0001) and 49 severely shocked patients (9.9 g/dL, p less than 0.00001). In 140 patients with systolic blood pressure (SBP) under 80 mm Hg on admission, mortality was increased in those with a Hb level under 8 g/dL (p less than 0.001), and a reduced mean Hb level was observed in 11 who died of hypovolemia (6.8 g/dL) compared with 6 dying of nonhypovolemic causes (11.7 g/dL), 10 dying of multiple causes (10.2 g/dL), or 113 survivors (11.7 g/dL, p less than 0.000001). In 31 patients with initial Hb levels of less than 8 g/dL, the overall mortality was 48.4%, compared with 2.6% in 969 patients whose initial Hb level was 8 g/dL or more (p less than 0.00001). Hypovolemia was judged to be the major factor in causing death in 13 (86.7%) of the 15 patients with a Hb level under 8 g/dL who died. A low Hb level observed soon after injury is usually an indicator of serious ongoing hemorrhage and has important implications for management and prognosis. Measurement of the Hb level may prove useful in prehospital assessment of the level of trauma care required and also in injury severity scoring as a predictor of mortality.