Intensive care unit (ICU) patients with acute kidney injury requiring renal replacement therapy (RRT) are considered at high risk of gastrointestinal (GI) bleeding and stress ulcer prophylaxis (SUP) is often prescribed. We aimed to assess the incidence of GI bleeding and effects of SUP in these patients.We assessed GI bleeding in ICU patients receiving RRT at baseline (and at any time in the ICU) and effects of prophylactic pantoprazole versus placebo in the international SUP in the ICU (SUP-ICU) trial. All analyses were conducted according to a published protocol and statistical analysis plan.Data of 3,291 acutely admitted adult ICU patients with one or more risk factors for GI bleeding randomized to pantoprazole or placebo intravenously once daily during ICU stay (until ICU discharge, death, or a maximum of 90 days) were analyzed. Some 20 out of 258 (7.8%, 95% CI 4.5-11.1%) and 52 out of 568 (9.2%, 95% CI 6.8-11.6%) of the patients receiving RRT at baseline and at any time in ICU, respectively, developed clinically important GI bleeding in the ICU. We did not observe statistically significant differences in the intervention effect (pantoprazole vs. placebo) in the proportion of patients with clinically important GI bleeding, clinically important events, infectious adverse events, use of interventions to stop GI bleeding, or 90-day mortality in patients with versus without RRT at baseline.In adult ICU patients receiving RRT at baseline, we observed high incidences of clinically important GI bleeding, but did not observe effects of pantoprazole versus placebo in this subgroup.