Out of 7,248 patients who underwent coronary artery bypass surgery from 1970-1995, 17% of females and 13% of males were severely obese, defined as body mass index (BMI) 30 kg/m2. Risk of death within 30 days of operation was 2.1% in patients with BMI < 25 kg/m2, 2.1% if BMI was 25-30 kg/m2 and 1.3% in patients with BMI 30 kg/m2 (P = 0.20). The low risk in obese patients persisted after multivariate correction for year of surgery, age, sex, hypertension, diabetes, unstable angina and number of diseased vessels. The risk of reoperation for bleeding decreased (P < 0.001) whereas the risk of wound infection and sternal dehiscence increased (P = 0.09 and P = 0.05, respectively) with increasing BMI. We conclude that coronary artery bypass surgery can be performed safely in obese patients.