BACKGROUND: Postoperative fever is common after cardiac surgery. In the absence of documented infection, atelectasis is often suggested as a cause of postoperative fever. However, this link is not well supported by pathophysiologic mechanisms. The purpose of this study was to investigate whether an association exists between atelectasis and postoperative fever in pediatric patients undergoing cardiac surgery. METHODS: A retrospective review was performed on consecutive pediatric patients who underwent cardiac surgery on cardiopulmonary bypass at a single cardiac surgery center from January 1, 2009, to December 31, 2009. Postoperative chest radiographs were evaluated and each lung was scored independently for atelectasis. Clinical parameters including the highest daily recorded temperature were noted and compared to atelectasis data. RESULTS: A total of 203 patients were enrolled; 139 patients (68.5%) had fever at least once during the first 3 postoperative days. The incidence of atelectasis on each day was 41%, 57%, and 71%, respectively. There was no association between fever and atelectasis on any postoperative day (P = .21). Microbiological cultures were performed on 81 patients, and infection was found in 7 patients (3.5%). The frequency of either fever or atelectasis was similar between cyanotic and acyanotic patients. CONCLUSIONS: Postoperative fever and atelectasis are both common after pediatric cardiac surgery. In our study, there was no significant association between postoperative fever and atelectasis. In children undergoing cardiac surgery with cardiopulmonary bypass, fever in the postoperative period should not be attributed to atelectasis.