Background: Coronary bypass grafts made with internal mammary artery have better long term results than those made with saphenous vein. It is possible that the use of both mammary arteries would lead to even better results. Aim: To compare the long term survival and the incidence of new coronary events of patients, in whom one or two mammary arteries were used as coronary bypass grafts. Patients and methods: One hundred and eight randomly selected patients who received one mammary artery for myocardial revascularization and 108 patients, matched for prognostic factors, who received two mammary arteries were studied. These patients were followed for a mean of 4 years (range 1 to 12 years). Operative complications, hospital mortality and long term probability of being free of disease were compared in both groups. Results: Operative mortality was similar in both groups (0,9%). Patients that received two mammary arteries had a higher frequency of operative wound complications. Long term survival was 84% in patients who received one and 83% in patients who received two mammary arteries. The probabilities of being free of myocardial infarction (92 and 82% respectively) and angina (94 and 86% respectively) were lower in the later group. Conclusions: Patients who received two mammary arteries had a higher probability of a long term disease free survival than patients who received one mammary artery.