Venous thromboembolism (VTE) prophylaxis is effective in reducing VTE events; however, it is underutilized in critically ill patients. We examined trends and risk factors for omission of early thromboprophylaxis within the first 24 h after admission in Australian and New Zealand intensive care units (ICUs) between 2009 and 2020.Retrospective analysis of data from the Australian New Zealand Intensive Care Society Adult Patient Database. Data were obtained for 1,465,020 adult admissions between 2009 and 2020. Mixed effects logistic regression modeling (accounting for the random effects of the contributing ICUs) was used to identify factors associated with omission of early thromboprophylaxis.A total of 107,486 (7.3%) ICU patients did not receive any form of thromboprophylaxis within the first 24 h after ICU admission without obvious reasons. Omission of early thromboprophylaxis declined from 13.7% in 2009 to 4% in 2020 (by 70.8%) (P < 0.001). Younger patients were more like to miss out on VTE prophylaxis (odds ratios (OR) 0.94, 95% CI 0.95-0.99). A documented process for monitoring VTE prophylaxis (ORs 0.90, 95% CI 0.87-0.93) and having a medical lead, dedicated for coordinating ICU quality (OR 0.97, 95% CI 0.93-0.99), are associated with less omission of VTE prophylaxis.per 10-year increaseOmission of thromboprophylaxis within the first 24 h after ICU admission has declined steadily over the past decade. Documented process for monitoring VTE prophylaxis and having a medical lead for coordinating quality of ICU care could be potential targets for sustaining the improvement in VTE prophylaxis use.