CONTEXT: Patients with mental disorders show higher burden of coronary heart disease, and may face special safety issues during in-hospital cardiac care. OBJECTIVES: To compare the postoperative complication rate between patients with and without mental disorders undergoing isolated coronary artery bypass graft (CABG) surgery. DESIGN, SETTING, AND PATIENTS: Retrospective analyses of New York state hospital claims between 1997 and 2004 (N=135,701). Complications were defined using the Agency for Healthcare Research and Quality Patient Safety Indicators (AHRQ PSI). PRINCIPAL FINDINGS: Mental disorders were significantly associated with higher anesthesia complications (adjusted odds ratio [AOR]=6.44, p < .001), decubitus ulcer (AOR=1.42, p = .006), postoperative hip fracture (AOR = 3.29, p < .001), and overall complication rate representing nine PSIs (AOR = 1.27, p < .001). CONCLUSIONS: Mentally ill patients undergoing CABG surgery are more likely to experience potentially preventable complications and injuries. The mechanism underlying this observation warrants further study.