Objective To test the diagnostic use of the triage white blood cell (WBC) count in differentiating major from minor injuries. Methods We conducted a retrospective study of a prospectively collected database of trauma patients 13 years of age or older at a Level I trauma center from January 2005 through December 2008. We excluded all patients with obvious life-threatening injuries requiring immediate surgery, isolated head trauma, transferred from another institution or dead on arrival. We recorded age, sex, injury mechanism, vital signs, WBC, base deficit (BD), lactate (LAC) and calculated injury severity scores (ISS). Major injury was defined as either a change in hematocrit >10 points or blood transfused within 24 hours, or ISS >15. Results 805 patients were included in the study with an average age of 38.6 years (Range 13–95 yrs) years. 75.3% of patients were male, 45.6% had blunt and 34.4% had penetrating trauma. For vital signs, blood pressure was not significantly different between major and minor injury patients. Major compared to minor injury patients had a statistically but not clinically significant higher heart rate. Major injury patients had significantly (p < 0.0001) higher WBC count (10.53 K/μl, 95% CI: 9.7–11.3) compared to patients with minor injuries (8.92 K/μl, 95% CI: 8.7–9.2), but both were in the normal range. Patients with major compared to minor injury had significantly (p < 0.0001) higher BD (−3.1 versus −0.027 mmol/L) and higher LAC (3.9 versus 2.48 mmol/L). Areas under the curve for WBC count (0.60, 95% CI: 0.54–0.66) are similar to BD (0.69, 95% CI: 0.63–0.74) and LAC (0.66, 95% CI: 0.60–0.71). Conclusion WBC count is not a useful addition as a diagnostic indicator of major trauma in our study population.