Many pediatric cardiac surgery centers obtain mediastinal cultures at the time of delayed sternal closure (DSC). There are no recommendations regarding how to treat patients with positive cultures. We explored the clinical significance of positive mediastinal cultures with regard to surgical site infections (SSI).A retrospective study was performed on all patients who underwent DSC at our institution between December 2006 and December 2011. National Healthcare Safety Network criteria were used to prospectively identify SSIs. Univariate and multivariate logistic regression analyses were performed to evaluate potential risk factors for SSI and predictors for positive mediastinal cultures obtained at DSC.A total of 178 patients underwent DSC during the study period; 155 patients met the eligibility criteria for the study and were included in the analysis. Of the 155 included patients, 11 patients (7.1%) experienced SSI. Patients with a positive mediastinal culture obtained at DSC were more likely to experience SSI than were patients with a negative culture (p=0.003). In univariate analysis, a positive mediastinal culture was the only factor associated with SSI (odds ratio [OR], 7.4; 95% confidence interval [CI], 2.1 to 26.7). In multivariate analysis, age at operation≥2 weeks (adjusted OR [aOR], 4.9; 95% CI, 1.84 to 12.8), receipt of stress-dosed hydrocortisone while the chest was open (aOR, 2.9; 95% CI, 1.1 to 7.6), and gestational age≤37 weeks (aOR, 2.7; 95% CI, 1.01 to 7.27) were independent predictors for a positive mediastinal culture.Patients with positive mediastinal cultures obtained at DSC had a significantly higher rate of subsequent SSI, and a positive mediastinal culture was the only statistically significant predictor of SSI.