Post-cardiac surgery pulmonary dysfunction may be underreported. Therefore, we evaluated associated risk factors for prolonged pulmonary support after cardiac surgery.We conducted a retrospective, observational study of consecutive patients undergoing coronary artery bypass grafting or coronary artery bypass grafting plus valve repair/replacement between Jan 1, 2005, and Dec 31, 2010, at an academic medical center. Using multivariate logistic regression and Cox proportional hazards modeling, we identified risk factors associated with prolonged mechanical ventilation and supplemental O2 support as well as in-hospital mortality.Overall, 33% (1298/3881) of patients required more than 2 days of mechanical ventilation and/or more than 5 days of supplemental O2 (prolonged support). Independent risk factors included age, weight, pre-existing lung disease, cardiac or renal dysfunction, emergent status, transfusion and cardiopulmonary bypass duration. Prolonged support was associated with increased mortality (OR, 4.75; 95% CI, 2.95-7.95; P < .001). Radiological evidence of persistent pulmonary edema 2 days after surgery was found in 4% of controls and 27% of prolonged support cases.We identified risk factors for prolonged mechanical ventilation and supplemental O2 use, described an association with increased adverse outcomes, and determined that persistent pulmonary edema on day 2 was the most likely radiological finding.