BACKGROUND: Reducing readmissions is a major healthcare reform goal, and reimbursement penalties are imposed for higher-than-expected readmission rates. Most readmission risk models and performance measures are based on administrative rather than clinical data. METHODS AND RESULTS: We examined rates and predictors of 30-day all-cause readmission following coronary artery bypass grafting surgery by using nationally representative clinical data (2008-2010) from the Society of Thoracic Surgeons National Database linked to Medicare claims records. Among 265 434 eligible Medicare records, 226 960 (86%) were successfully linked to Society of Thoracic Surgeons records; 162 572 (61%) isolated coronary artery bypass grafting admissions constituted the study cohort. Logistic regression was used to identify readmission risk factors; hierarchical regression models were then estimated. Risk-standardized readmission rates ranged from 12.6% to 23.6% (median, 16.8%) among 846 US hospitals with ≥30 eligible cases and ≥90% of eligible Centers for Medicare and Medicaid Services records linked to the Society of Thoracic Surgeons database. Readmission predictors (odds ratios [95% confidence interval]) included dialysis (2.02 [1.87-2.19]), severe chronic lung disease (1.58 [1.49-1.68]), creatinine (2.5 versus 1.0 or lower:1.49 [1.41-1.57]; 2.0 versus 1.0 or lower: 1.37 [1.32-1.43]), insulin-dependent diabetes mellitus (1.45 [1.39-1.51]), obesity in women (body surface area 2.2 versus 1.8: 1.44 [1.35-1.53]), female sex (1.38 [1.33-1.43]), immunosuppression (1.38 [1.28-1.49]), preoperative atrial fibrillation (1.36 [1.30-1.42]), age per 10-year increase (1.36 [1.33-1.39]), recent myocardial infarction (1.24 [1.08-1.42]), and low body surface area in men (1.22 [1.14-1.30]). C-statistic was 0.648. Fifty-two hospitals (6.1%) had readmission rates statistically better or worse than expected. CONCLUSIONS: A coronary artery bypass grafting surgery readmission measure suitable for public reporting was developed by using the national Society of Thoracic Surgeons clinical data linked to Medicare readmission claims.