We identified 810 reports that describe extracorporeal membrane oxygenation (ECMO) in acute respiratory distress syndrome (ARDS), and 61 fulfilled our inclusion criteria. The authors of 26 (43%) reports responded to e-mail requests for confirmation (or clarification). Based on the aggregate (published and e-mailed) information, unambiguous data were available relating to 17 papers. These 17 papers represented 672 patients with ARDS who were cannulated with venovenous ECMO; of these patients, 208 (31%) received a trial of prone positioning before ECMO, and 464 (69%) did not. A key randomized controlled trial was published in 2013 that reported a survival benefit associated with prone positioning (N Engl J Med 2013;368:2159-2168). The proportion of all venovenous ECMO patients in whom prone positioning was used before ECMO was lower in studies published after 2013 (84 of 452 [19%]) than in those published before 2013 (116 of 210 [55%]) (P < 0.05). These data suggest a systematic bias in the reporting of outcomes after ECMO in the literature. The vast majority of reported patients who received ECMO did not first receive therapy that (in contrast to ECMO) is simple, cheap, and of proven benefit; therefore, inferences about the efficacy of ECMO in ARDS are of limited use.