objective: mediastinitis is a serious complication of median sternotomy and is associated to significant morbidity and mortality. the aim of this study is to identify risk factors for mediastinitis in patients undergoing coronary artery bypass grafting (cabg), without the use of bilateral internal thoracic artery (ita), at the division of cardiovascular surgery of pronto socorro cardiológico de pernambuco - procape. methods: a retrospective study of 500 consecutive patients operated on between may 2007 and april 2010. ten preoperative variables, seven intraoperative variables and seven postoperative variables possibly involved in the development of postoperative mediastinitis were evaluated. univariate and multivariate logistic regression analyses were performed. results: the incidence of mediastinitis was 5.6% (n=28), with a lethality rate of 32.1% (n=9). in multivariate analysis using logistic regression, five variables remained as independent risk factors: obesity (or 2.60, 95% ci 1.11 to 6.68), diabetes (or 2.71, 95% ci 1.18 to 6.65), smoking (or 2.10, 95% ci 1.12 to 4.67), use of pedicled internal thoracic artery (or 5.17, 95% ci 1.45 to 18.42) and on-pump cabg (or 2.26, 95% ci 1.14 to 5.85). conclusion: this study identified the following independent risk factors for mediastinitis after cabg: obesity, diabetes, smoking, use of pedicled ita and on-pump cabg.