We prospectively followed 446 consecutive patients who had coronary bypass operations 15 years earlier. Serum levels of cholesterol and triglycerides were measured before and 5 years after bypass, and we established the relation between these lipid levels and the incidence of myocardial infarction (MI) and cardiac mortality during 15 years of follow-up. Follow-up was complete in 99.8% of the patients and averaged 15.4 years for the survivors. Multivariate Cox proportional-hazards analysis revealed that patients with preoperative hypertriglyceridemia (> or = 2.0 mmol/L [176 mg/dl]) had a 2.1 times increased risk for MI during follow-up (p = 0.04). Hypertriglyceridemic patients 5 years after surgery had a 2.2 times increased risk for MI during the subsequent follow-up period, although this difference was not statistically significant (p = 0.09). The only significant risk factor for MI 5 years after surgery was smoking. Hypercholesterolemia (> or = 6.5 mmol/L [254 mg/dl]) both before and 5 years after surgery was not a risk factor for MI during follow-up. Cardiac mortality was not significantly related to either hypercholesterolemia or hypertriglyceridemia. Independent predictors for cardiac mortality were poor left ventricular function, diabetes mellitus, incomplete revascularization, and the use of sequential bypass grafts. These data provide evidence that hypertriglyceridemia, both before and 5 years after surgery, have predictive value for the incidence of MI during long-term follow-up after venous coronary bypass surgery.