In this review, we examine outcomes from using high-frequency ventilation compared with conventional ventilation as therapy for acute lung injury and acute respiratory distress syndrome in children and adults. We conducted a systematic search of the literature based on the guidelines of the Cochrane Collaboration. Two trials met the inclusion criteria; one recruited children (n = 58), and the other recruited adults (n = 148). Both trials used a high-frequency oscillatory ventilator as the intervention and included variable use of lung-volume recruitment strategies. The intervention groups showed a trend toward less 30-day mortality (children: relative risk [RR], 0.83; 95% confidence interval [CI], 0.43-1.62; adults: RR, 0.72; 95% CI, 0.50-1.03), although neither study showed a statistically significant difference. Similarly, there was no statistically significant difference between the intervention and control groups for "total length of ventilator days." There was a statistically significant reduction in the risk of requiring supplemental oxygen among survivors at 30 days in the pediatric study (RR, 0.36; 95% CI, 0.14-0.93). Overall there is not enough evidence to conclude that high-frequency ventilation reduces mortality or long-term morbidity in patients with acute lung injury or acute respiratory distress syndrome. (This review is published as a Cochrane Review in The Cochrane Library 2004, Issue 3. Cochrane Reviews are regularly updated as new evidence emerges and in response to comments and criticisms, and The Cochrane Library should be consulted for the most recent version of the Review.).