&NA;Extravascular lung water (EVLW) was measured by the double‐indicator dilution method in 25 patients with hemorrhagic cerebrovascular diseases. EVLW had a significantly positive correlation with both alveolar‐arterial oxygen difference (AaDO2) and intrapulmonary shunt. The value of EVLW in the acute stage in 15 patients with increased AaDO2more than 20 mm Hg was 7.8 ± 2.2 ml/kg and that in the chronic stage 4 weeks after onset significantly decreased to 4.6 ± 0.7 ml/kg (P< 0.001). The value of EVLW in the acute stage in 10 patients with normal AaDO2less than 20 mm Hg was 4.7 ± 1.1 ml/kg and that in the chronic stage 4 weeks after onset was 4.5 ± 0.2 ml/kg. There was no significant difference between them. Pulmonary arterial blood pressure, pulmonary capillary wedge pressure, central venous pressure, cardiac index, systemic vascular resistance index, and pulmonary vascular resistance index in the acute stage in the 25 patients were all within the normal range. Three patients with neurogenic pulmonary edema had markedly increased EVLW without abnormalities in pulmonary arterial blood pressure, pulmonary capillary wedge pressure, central venous pressure, cardiac index, systemic vascular resistance index, and pulmonary vascular resistance index. From these facts, the main cause of the increase in EVLW cannot be explained by left ventricular failure, but can be explained by high permeability pulmonary edema. (Neurosurgery25:762‐768, 1989)