BackgroundProne positioning is a historically underutilized evidence-based practice for acute respiratory distress syndrome (ARDS). Despite increased prone positioning during the COVID-19 pandemic, some patients may remain at risk of non-use. Research QuestionWhat is the current evidence-based gap for prone positioning in ARDS, how is use changing over time, and what are patient level barriers and facilitators to prone positioning. Study Design and MethodsThis retrospective cohort included invasively ventilated adults with ARDS and who met prone positioning criteria from six hospitals. The rate of prone positioning among eligible patients was summarized January 2018 to December 2021. Segmented Poisson regression was used to describe temporal trends. Logistic regression was used to identify patient level barriers and facilitators to prone positioning. Results799 patients fulfilled criteria for prone positioning; mean age 57 years, 125 (15.6%) COVID-19, intensive care stay 19.5 days and mortality 50.1%. Prone positioning was used in 297/799 (37.2%) patients. Prone positioning was increasing pre-pandemic with relative rate (RR) 1.12 per quarter (95% Confidence Interval [CI] 1.03 – 1.22). Prone positioning increased during the pandemic vs. pre-pandemic (RR 1.62, 95%CI 1.02 – 2.61), but not for patients with non-respiratory diagnoses (RR 0.74, 95%CI 0.22 – 2.52). Barriers to prone positioning included vasopressor use (odds ratio [OR] for withholding prone 1.15 per 0.1 mcg/kg/min norepinephrine equivalent, 95%CI 1.06 – 1.26), age (OR 1.12 per 5 years, 95%CI 1.03 – 1.22), and being post-operative (OR 2.41, 95%CI 1.00 – 5.81). Facilitators included having COVID-19 (OR for withholding prone 0.10, 95%CI 0.04 – 0.24) or another respiratory illness (OR 0.42, 95%CI 0.23 – 0.79), and receiving neuromuscular blockade (OR 0.22, 95%CI 0.13 – 0.38). Interpretation:Despite increased prone positioning during the COVID-19 pandemic an evidence-based gap persists, especially for patients with non-respiratory causes of ARDS. There are multiple barriers and facilitators to target to increase prone positioning.