BACKGROUND: The relationship between fibrinogen concentration and traumatic death has been poorly explored after severe trauma. Existing studies analysed this relationship in unselected trauma population, often considering fibrinogen concentration as a categorical variable. The aim of our study was to model the relationship between fibrinogen concentration and in-hospital mortality in severe trauma patients requiring massive transfusion using fibrinogen on admission as a continuous variable. METHODS: We designed a retrospective observational study based on prospectively collected data from 2009 to 2015 in seven French level-I trauma centres. All consecutive patients requiring a transfusion of at least 10 packed red blood cells (RBC) within 24 h were included. To assess the relationship between in-hospital death and fibrinogen concentration on admission, we performed generalized linear and additive models with death as a dependent variable. We also assessed the relationship between fibrinogen concentration below 1.5 g.L- 1 and potential predictors. RESULTS: Within the study period, 366 patients were included. A non-linear relationship was found between fibrinogen concentration and death. Graphical modelling of this relationship depicted a negative association between fibrinogen levels and death below a fibrinogen concentration of 1.5 g.L- 1. Predictors of low fibrinogen concentration (< 1.5 g.L- 1) were systolic blood pressure, Glasgow coma scale and haemoglobin concentration on admission. CONCLUSIONS: A complex and robust approach for modelling the relationship between fibrinogen and mortality revealed a critical fibrinogen threshold of 1.5 g.L- 1 for severe trauma patients requiring massive transfusion. This trigger may guide the administration of procoagulant therapies in this context.