Objective:To determine if there is a correlation between an increase in glomerular permeability, the magnitude of trauma, and the severity of illness.Design:Prospective study.Setting:Two university hospital intensive care units.Patients:Forty consecutive critically ill trauma patients admitted directly to the intensive care unit within 120 mins of their injuries.Interventions:None.Measurements and Main Results:For each patient, urine was collected from the time of admission until 7 am the next day. Within 48 hrs, only one sample of all urine collected (5 mL) was examined for microalbuminuria and urinary creatinine. Results were expressed as the microalbuminuria/urinary creatinine ratio (MACR). The mortality rate in the intensive care unit, Injury Severity Score at the moment of admission, Acute Physiology and Chronic Health Evaluation III score, and Simplified Acute Physiology Score in the first 24 hrs were calculated for each patient. The data were analyzed using the Pearson test for linear regression and Student'st-test. During the first 24 hrs after trauma, there was an increase of MACR (6.9 ± 0.6 mg/mmol) above normal (reference range, <3 mg/mmol) that was positively correlated with Injury Severity Score (31.4 ± 1.9; r2= .73,p< .05). However, there was no correlation between MACR, Acute Physiology and Chronic Health Evaluation III score, Simplified Acute Physiology Score, and mortality rate.Conclusions:Patients with trauma show an increase in glomerular permeability during the first 24 hrs after injury. The magnitude of this increase is correlated with the extent of trauma but does not seem significant enough to be predictive of severity of illness and/or outcome.