Base deficit (BD) is a prognostic tool that correlates with trauma scores and mortality in adult trauma patients. Retrospective studies have shown that admission BD more than 8 mmol/L is associated with an increased risk of mortality. This is the first prospective European study aimed at evaluating the prognostic value of admission BD in traumatized children.One hundred severely traumatized children were included if an arterial BD had been calculated on arrival in the trauma room of a university hospital. Epidemiologic, medical, and biological data (including admission BD and lactates concentration) were recorded and compared using a univariate analysis. The primary endpoint was in-hospital mortality. Secondary endpoints were outcome on discharge and at 6 months. Cutoff values for BD or lactates regarding outcomes were determined using receiver operating characteristic curves if these data had been isolated on multivariate analysis (p0.05).Sixty-eight boys and 32 girls, aged 6.7 years, were enrolled from March 2003 to December 2005, mainly after road traffic accidents. Twenty-two died at the hospital, 34 children and 51 children were classified as having a good outcome on hospital discharge and 6 months later, respectively. After the multivariate procedure and receiver operating characteristic curve analysis, admission lactates more than 2.94 mmol/L and admission BD more than 5 mEq/L were independent risk factors for mortality (odds ratio 2.4 [95% confidence interval 1.3-4.6]) and poor outcome at 6 months (odds ratio 2.5 [95% confidence interval 1.13-5.5]), respectively.BD could be used to predict the long-term morbidity and may not be related to morbidity and mortality at discharge.