This study examined the effect of fluid balance on survival in ARDS. Of the 213 patients entered into a prospective data collection study, we evaluated 113 patients who met strict criteria for ARDS. Multiple variables were analyzed for as long as 14 days after intubation including cardiac output, pulmonary capillary wedge pressure, mean blood pressure, intake minus output (I-O), cumulative intake minus output (cum I-O), and change in weight (delta wt). We found significant differences in cum I-O and delta wt between survivors and nonsurvivors on almost every day. Survivors lost weight and had a significantly lower cum I-O compared with nonsurvivors. Logistic regression was used to determine if delta wt and cum I-O could predict survival. Patients who lost 3 kg or more weight had a much higher survival than did those who gained 3 kg or more weight (67 and 0%, respectively, on Day 14). Similar results were obtained using comparably low and high values for cum I-O. The logistic regression equations demonstrated that weight loss and low cumulative I-O correlated with improved survival. Although cause and effect relationships are difficult to determine from these types of analyses, they can be used to formulate prospective studies and predict survival in patients.