Airway pressure release ventilation (APRV) is a ventilatory mode that allows unsupported spontaneous breathing at any phase of the ventilatory cycle with high mean airway pressures. We hypothesized that use of APRV might produce potential beneficial effects on oxygenation, reducing mortality in patients with severe acute respiratory distress syndrome (ARDS) in comparison with synchronized intermittent mandatory ventilation (SIMV) as a conventional mode of ventilation. We retrospectively reviewed data of 58 patients with severe ARDS (the ratios of partial arterial oxygen tension to fraction of inspired oxygen, PaO2/F(I)O2 ratio <150). The patients' data were divided into two groups: SIMV-group and APRV-group. Patients' backgrounds, oxygenation on day 0, 1, 3, 5 and 7 following initiation of each mode, vasopressor dependence, duration of ventilation, duration of ICU stay, and mortality in ICU were analyzed. PaO2/F(I)O2 ratios were statistically higher in the APRV-group (APRV vs. SIMV on day 1, 3, 5, 7: 201.6 +/- 76 vs.150 +/- 59.1, 256.7 +/- 71.5 vs.182.1 +/- 65.4, 268.8 +/- 73.3 vs. 204.6 +/- 72.8, and 263 +/- 74.5 vs. 204.1 +/- 67.1, respectively, p<0.05). Vasopressors were less used (p=0.018), and mortality in ICU tended to be lower in the APRV group (31%) than in the SIMV group (59%) (p=0.050). Use of APRV in patients with severe ARDS appears to be associated with improvements in oxygenation, and a trend toward lower mortality in ICU. No significant adverse effects were observed. Prospective controlled studies are required to confirm the benefits of this ventilatory mode in comparison with conventional methods for severe ARDS.