The internal mammary artery (IMA) has been widely used in CABG due to the excellent long-term results. However, the extensive use of bilateral IMA grafting has been believed to increase operative morbidity and mortality. This study was designed to determine if bilateral IMA grafting in diabetic patients increased the likelihood of mediastinitis. We analyzed the data of 386 consecutive patients who underwent isolated CABG in 1992 to 1996. The definitions of sternal wound complications are as follows, (1) mediastinal dehiscence and (2) mediastinal wound infection. Subtypes include superficial wound infection and deep wound infection (mediastinitis). Among these patients 97 received unilateral IMA grafts and 289 did bilateral IMA grafts. mediastinitis did not occur in any subjects. The occurrence rate of mediastinal dehiscence and superficial wound infection was 7.2% (7/97) for bilateral IMA grafting, 7.3% (21/289) for unilateral IMA grafting. No patients died of wound complications. The occurrence rate of mediastinal dehiscence and superficial wound infections were 12.0% (4/33) for bilateral IMA grafting in diabetic patients, 12.0% (14/117) for unilateral IMA grafting in diabetic patients. That of this complications was 4.7% (3/64) for bilateral IMA grafting in non-diabetic patients, 4.1% (7/172) for unilateral IMA grafting in diabetic patients, without significant differences in wound complication. Bilateral IMA grafting in diabetic patients carried no great risk of mediastinitis, but diabetes mellitus itself was a great risk for mediastinitis.