Between 1984 and 1991, 30 patients developed poststernotomy mediastinitis after cardiac or mediastinal operations. Sixteen of these patients were treated with debridement and open drainage or primary closure following mediastinal irrigation (drainage group). Fourteen patients were treated with debridement, and delayed or primary wound closure by the technique of pectoral or rectus abdominus muscle flap mobilization (muscle flap group). The purpose of this study was to compare the results of the different treatment of poststernotomy mediastinitis. Although the pre- and perioperative profile, complications and risk factors for mediastinal infection were the same, the mortality of muscle flap group was significantly lower than that of drainage group (Fisher exact probability test, p < 0.05). Pulmonary function of the patients who received muscle flap mobilization did not decrease from the function before surgery, despite the defect of sternal bony stabilization. We conclude that muscle flap mobilization may be a superior method as the treatment for poststernotomy mediastinitis after cardiac operations, and may not decrease respiratory function of the patients.