Perioperative myocardial injury (PMI) after coronary revascularization (bypass surgery using cardiopulmonary bypass or percutaneous intervention) is strongly associated with future adverse events, such as death, myocardial infarction, and coronary intervention. The incidence, determinants, and prognostic significance of PMI after bypass surgery without cardiopulmonary bypass (off-pump surgery) are unknown. The study population comprised the patients who were randomized to off-pump surgery in the Octopus Study. PMI was defined by a creatine kinase isoenzyme-MB/total creatine kinase ratio of >5% during the first 48 hours, postoperatively. PMI occurred in 137 of 260 patients (52%). Using multivariate regression analysis, age, female gender, previous myocardial infarction, preoperative nitrate use, preoperative diuretic use, and number of grafts were independently associated with an increased risk of PMI during off-pump surgery. The presence of preoperative coronary collaterals showed a negative association with PMI. The occurrence of PMI had a crude odds ratio of 7.53 (95% confidence interval 1.59 to 35.63) for an adverse cardiac event at 1 year after off-pump surgery. This odds ratio changed little after adjustment for confounders (odds ratio 6.39, 95% confidence interval 1.41 to 28.93). In conclusion, more severe atherosclerotic disease and female gender were associated with an increased risk of perioperative myocardial injury during off-pump bypass surgery, although the presence of coronary collaterals appeared to be protective. Patients with perioperative myocardial injury during off-pump surgery were at a higher risk of adverse cardiac outcomes at 1 year.