BACKGROUND: Transfusion-associated circulatory overload (TACO) is a growing concern in clinical practice. STUDY DESIGN AND METHODS: A case controlstudy was performed at the Nîmes University Hospital, France. TACO cases occurring after RBC transfusion reported from January 1, 2014, to May 31, 2017, were included as cases. Four controls by case were randomly selected among the other RBC recipients on the same day. RESULTS:During the study period, 60 TACO diagnoses were reported for 37,029 transfused RBCs to a total of 8787 patients; 240 controls were included. The average rate of TACO was one case every 616 RBCs transfused. One in 146 transfused patients experienced TACO. TACO was associated with a higher 28-day mortality (22% vs. 11%; p = 0.003), and a longer hospital stay compared with controls (23.5 AE 19.6 days vs. 15.9 AE 20.1 days; p < 0.001). Four risk factors were independently associated with TACO in multivariable analysis: chronic use of loop diuretics (odds ratio [OR], 6.5, 95% confidence interval [CI], 3.3-12.9), hemorrhagic shock (OR, 12; 95% CI, 2.9-50), body weight <46 kg (OR, 7.9; 95% CI, 2.3-26.8) and chronic hypertension (OR, 4.1; 95% CI, 2-8.5). CONCLUSION: TACO was frequent and associatedwith poor outcome. Four independent risk factors were identified: hemorrhagic shock, low body weight, chronic use of diuretics, and chronic hypertension.* Median (interquartile range).† Over a 24-hour period. ‡ Mean AE standard deviation (SD). TACO, transfusion-associated circulatory overload. All results are presented as absolute number (%) unless otherwise indicated.