Background: Although the association of neutrophil proportions with mortality in trauma patients has recently been shown, there is a paucity of research on the association with other outcomes. We sought to investigate the association of neutrophil proportions with organ failure in critically-ill trauma patients. Methods: We reviewed a randomly-selected group of trauma patients admitted to our level-1 trauma intensive care unit between July 2007 and December 2016. Data collected included demographics, injury mechanism and severity (ISS), neutrophil-to-lymphocyte ratio (NLR) at admission and at 24 and 48 hours and organ failure data. NLR patterns during the first 48 hours were divided into two trajectories identified by applying factor and cluster analysis to longitudinal measures. Logistic regression was performed for the association between NLR trajectories and any organ failure; negative binomial regression was used to model the number of organ failures and stage of kidney failure measured by KDIGO classification. Results: 207 patients had NLR data at all three time points. The average age was 44.9 years with mean ISS of 20.6. Patients were 72% male and 23% had penetrating trauma. The 74 patients (36%) with Trajectory 1 had a mean NLR at admission of 3.6, which increased to 14.7 at 48 hours. The 133 (64%) patients in Trajectory 2 had a mean NLR at admission of 8.5 which decreased to 6.6 at 48 hours. Mean NLR was different between the two groups at all three time points (all p < 0.01). There was no significant difference in ISS, age or gender between the two trajectory groups. Models adjusted for age, gender and ISS showed that relative to those with trajectory 2, patients with the trajectory 1 were more likely to have organ failure OR 2.96 (1.42⁻6.18; p < 0.01), higher number of organ failures IRR 1.50 (1.13⁻2.00, p < 0.01), and degree of AKI IRR 2.06 (1.04⁻4.06, p = 0.04). In all cases, the estimated associations were higher among men vs. women, and all were significant among men, but not women. Conclusions: Trauma patients with an increasing NLR trajectory over the first 48 hours had increased risk, number and severity of organ failures. Further research should focus on the mechanisms behind this difference in outcome.