BACKGROUND: Mediastinitis is a complication of coronary artery bypass graft surgery (CABG) that can be difficult to diagnose. This study evaluated the utility of blood culture results in identifying patients with mediastinitis. METHODS AND RESULTS: All unique patients undergoing CABG at our institution over a 60-month study period (n=5500) and all blood cultures performed on these patients or=1 blood culture drawn within 90 days of CABG. Mediastinitis occurred in 46 of 60 (76.7%) patients with blood cultures positive for Staphylococcus aureus, 15 of 126 (11.9%) patients with blood cultures positive for other pathogens, 37 of 669 (5.5%) patients with blood cultures with no growth, and 44 of 4645 (0.9%) patients with no blood cultures obtained. The isolation of S aureus from even 1 blood culture drawn after or=1 blood culture obtained after CABG. CONCLUSIONS: Among patients with blood cultures drawn after CABG, S aureus bacteremia strongly suggests the presence of mediastinitis.