Although the utility of the base deficit as an indicator of hypoperfusion and physiologic derangement in adults is well established, its value in the assessment of children is not as clear. The purpose of this study was to evaluate this tool with regard to injury severity, infectious morbidity, and outcome in a pediatric trauma population. A retrospective review of a 6-year period of the database of our level 1 pediatric trauma center was performed. One hundred seventeen severely injured children requiring mechanical ventilation were identified. Initial base deficit, Injury Severity Score, time to correction of this abnormality, ventilator days, infectious morbidity, and mortality were obtained and compared. Of the 117 patients included in this study, 30 patients were identified with an initial BD of less than or equal to -8 mEq/L and were placed into group 1. Group 2 consisted of the remaining 87 patients who presented with a base deficit (BD) of greater than -8 mEq/L. An admission base deficit of -8 mEq/L or less corresponded to a probability of mortality of 23 per cent as opposed to only 6 per cent with a BD greater than -8. Patients in group 1 remained on mechanical ventilation 9.4 +/- 8.1 days, whereas patients in group 2 remained ventilated 6.5 +/- 6.4 days; an increase of nearly 145 per cent. Likewise, the number of infectious complications rose 26 per cent with a worsening initial base deficit from 17 per cent of group 2 patients to 43 per cent of group 1 patients. We conclude that a high initial base deficit in injured children predicts a higher incidence of infectious complications and a less favorable outcome. This readily available laboratory study can identify those children most at risk of potentially preventable complications.