In critically ill patients, capillary leakage often occurs which in the lungs may lead to pulmonary edema by increased microvascular pressure and permeability. However, clinical assessment of the extent of pulmonary capillary leakage and pulmonary edema is difficult. Several decades ago, the transpulmonary double indicator (thermo-dye) dilution technique has been introduced for quantification of extravasastion of fluids in the lungs by determination of the extravascular lung water (EVLW). The thermo-dye is based on simultaneous central venous injection of a freely diffusible indicator (‘cold’) and a plasma-bound indicator (indocyanine green). This technique has been extensively validated in animal experiments using post-mortem gravimetry and in humans using radionuclide techniques. However, the thermo-dye dilution technique is relatively expensive and time consuming therefore assessment of EVLW is increasingly performed by single transpulmonary thermodilution, which according to animal experimental and clinical studies is sufficiently accurate for estimation of EVLW. Using EVLW to guide the management of patients with both cardiac and non-cardiac pulmonary edema (ARDS) has been shown to reduce the duration of mechanical ventilation, length of stay in the intensive care unit and potentially intensive care costs. EVLW-guided therapy also reduced mortality in those patients with congestive heart failure and ARDS. Recent clinical studies have shown that in critically ill patients EVLW correlates with the severity of lung injury and that it does have a prognostic value. Thus, monitoring EVLW can be a useful additional tool in the goaldirected therapy of critically ill patients, especially those with severe sepsis and sepsis-induced acute lung injury.