['Von Willebrand factor antigen (vWF-Ag) is a marker of pulmonary and systemic endothelial activation and injury. Adult studies indicate that patients with plasma vWF-Ag levels > or = 450% of control early in the course of acute lung injury (ALI) have an increased risk of death. The objective of this study was to evaluate whether vWF-Ag is elevated in the early phase of ALI in children and whether the magnitude of the increase was predictive of two important outcomes: mortality or duration of mechanical ventilation.', 'Two-center, prospective observational study.', "Two pediatric intensive care units: one in an academic university setting and one in a major community children's hospital.", 'After appropriate consent, plasma was collected from 48 pediatric patients on day 1 of ALI, 45 patients on day 2 of ALI, and four intubated controls.', 'None.', 'Mean PaO2/FiO2 at the onset of ALI was 140 +/- 70, and mortality rate was 17%. vWF-Ag levels on day 1 of ALI were higher in patients compared with controls (287 +/- 183 vs. 87 +/- 84% of control [mean +/- SD], p < .05). Patients with vWF-Ag levels > or = 450% of control on day 1 of ALI had a markedly greater risk of death (odds ratio, 7.0; confidence interval, 1.31, 37.30; p < .05). Multivariate analysis revealed that elevated vWF-Ag level and either presence of multiple organ system failure or Pediatric Risk of Mortality III score independently predict increased risk of death. vWF-Ag levels on day 2 of ALI were significantly higher in patients who required prolonged mechanical ventilation (316 +/- 173 vs. 191 +/- 89% of control, p < .05).'] Is early elevation of plasma von Willebrand factor antigen in pediatric acute lung injury associated with an increased risk of death and prolonged mechanical ventilation?