Importance: Blood transfusion can be a lifesaving treatment for the surgical patient, yet transfusion-related immunomodulation may underlie the association of allogeneic transfusion with increased perioperative morbidity and possibly poorer long-term oncologic outcomes., Objective: To evaluate trends in transfusion rates for major abdominal oncologic resections to assess changes in recent clinical practice (given the accumulating evidence of the deleterious effects of blood transfusion)., Design, Setting, and Participants: Retrospective review of a population-based registry of all hospitals participating in the American College of Surgeons National Surgical Quality Improvement Project (2005-2013 Participant Use Data Files), which was queried for patients who underwent major resection of a pancreatic, hepatic, or gastric malignant tumor. Data analysis was performed from July to August 2015., Main Outcome and Measures: The primary outcome was the transfusion of any quantity of packed red blood cells. Transfusion rates were calculated for the perioperative period, which was defined as the time from the start of surgery to 72 hours after surgery. Secondary outcomes included wound infection, myocardial infarction, and renal insufficiency, and the rates of these complications were calculated as well. Trend analysis was performed for each year of data to evaluate for changes over the study period., Results: A total of 19 680 patients (median age, 65.0 years [interquartile range, 57.0-73.0 years]) were identified, of whom 5900 (30.0%) received a blood transfusion (of 13 657 patients who underwent a pancreatic resection, 4074 required transfusion [29.8%]; of 1605 patients who underwent a gastric resection, 378 required transfusion [23.6%]; and of 4418 patients who underwent a hepatic resection, 1448 required transfusion [32.8%]). There was a significant trend toward decreasing rates of transfusion during the study period (z = -7.89, P < .001), which corresponded to an absolute 6.1% decrease in the rate of transfusion of packed red blood cells from 2005 to 2013 (ie, from 32.8% to 26.7%). There was no significant change in the rates of postoperative wound infection or renal insufficiency during this time period, but there was an increased rate of perioperative myocardial infarction during the study period (0.33% absolute increase; z = 3.15, P = .002)., Conclusions and Relevance: Over 9 years of contemporary practice, a trend of less perioperative blood transfusions for oncologic abdominal surgery was observed. Further studies are needed to assess whether these trends reflect changes in operative techniques, hospital cohorts, or transfusion thresholds.