OBJECTIVE: Previous studies on risk factors for postoperative surgical site infections (SSI) have identified presence of diabetes as a major risk factor for development of SSI following cardiac surgery. However, why certain diabetics are more likely to develop SSI than others is unknown. The purpose of this study was to identify risk factors and outcomes of SSI in diabetics undergoing cardiac surgery. METHOD: Nested, case-control study. Patients with diabetes undergoing coronary artery bypass or valve replacement surgery at St. Luke's Episcopal Hospital, Houston, Texas, who experienced a post-operative SSI (n=71) in 2002-2004 were compared to randomly selected, uninfected controls (n=103) whom underwent similar surgery during the same time period. Clinical data was collected to determine risk factors and outcomes using univariate statistics and multivariate logistic regression. RESULTS: History of cardiac disorders (congestive heart failure, stroke, angina, or myocardial infarction) (OR = 1.589; 95% CI =1.132-2.230; p=0.0075) and obesity (OR = 2.849; 95% CI =1.241-6.542; p=0.0136) were identified as significant independent risk factors for SSI in diabetics undergoing cardiac surgery. Cases were hospitalized an average eight-days longer than uninfected controls (p=0.0006) and experienced twice as many complications requiring reoperation (10.6% vs. 21%; p=0.057). CONCLUSION: Cardiac history and obesity were identified as significant risk factors for SSI in our diabetic patient population. SSI significantly increased hospital length of stay in our diabetic population.