OBJECTIVE To investigate the prognostic value of extravascular lung water index (EVLWI) in critically ill patients with septic shock in intensive care unit (ICU). METHODS EVLWI was determined by using a PiCCO Monitor, and the daily fluid balance was recorded. RESULTS Fifty patients with septic shock were admitted and twenty-six patients survived. The average EVLWI at baseline was 11.7 ml/kg, and the difference was not different between survivors and nonsurvivors, P = 0.551. The EVLWI of day 3 (EVLWI(d3)) in nonsurvivors was significantly higher than the survivors [(14.3 +/- 8.8) ml/kg vs (8.1 +/- 2.7) ml/kg, P = 0.001]. If the patients were divided into three groups by the EVLWI(d3), group one 0-7 ml/kg (4/16), group two 8-14 ml/kg (10/24), and group three > 14 ml/kg (10/10), the hospital mortality of the third group was significantly higher than the other two groups (P = 0.000, 0.002). There was a significant difference between the survivors and the nonsurvivors in the fluid balance at the first day and the following three days (P = 0.000, 0.000). Negative fluid balance was associated with a lower mortality. By using receiver operating characteristic analysis, the area under the curve was 0.740 +/- 0.072 to EVLWI(d3). If EVLWI > 7.5 ml/kg, the sensitivity and the specificity of accurate judgment were 83.3% and 53.8%. CONCLUSIONS Dynamic observation of EVLWI can be one of the factors for predicting the prognosis of patients with septic shock. A reduction of EVLWI at early treatment and a negative fluid balance were associated with a better prognosis.