['Massive intraoperative transfusion is associated with increased morbidity and mortality in patients undergoing noncardiac thoracic operations. We examined whether this association carries over to patients who receive only 1 to 2 units of packed red blood cells (PRBCs) during their operation.', "We queried the American College of Surgeon's National Surgical Quality Improvement Project database for patients undergoing noncardiac, nonvascular thoracic operations during a 5-year period. Patient 30-day morbidity (1 or more of 20 complications) and mortality were evaluated. We used propensity-score matching to minimize confounding when estimating the effect of transfusion on postoperative morbidity.", 'We analyzed 8728 nonvascular thoracic operations in patients from 173 hospitals. Of these, 7875 (90.2%) did not receive intraoperative transfusions. The 579 patients (6.6%) who received 1 to 2 units of intraoperative PRBCs had higher unadjusted rates of wound problems, pulmonary complications, sepsis/shock, composite morbidity, mortality, and length of stay than those who did not receive transfusions. These rates further increased with postoperative transfusion of more than 2 units of intraoperative PRBC. After propensity adjustment, transfusion of 1 or 2 units of PRBCs increased the multivariate risk of composite morbidity, pulmonary complications, systemic sepsis, wound complications, and the postoperative length of stay compared with those who did not receive transfusions.'] Does intraoperative transfusion of small amounts of blood herald worse postoperative outcome in patients having noncardiac thoracic operations?