The use of bilateral in situ internal thoracic arteries is restricted by the risk of sternal devascularization, the length of the pedicle, and the necessity to avoid crossing the midline. The aim of this study is to evaluate Y grafts achieved by anastomosing the proximal end of the free right internal thoracic artery to the side of the attached left internal thoracic artery. Y grafts were performed in 80 patients, aged 41 to 74 years (mean age 58.6 years) between May 1991 and September 1992. Two different techniques were used. Thirty-four patients were included in group 1 and 46 in group 2. Seventy-nine grafts were performed from the left internal thoracic artery to the left anterior descending artery. The right internal thoracic artery was anastomosed to the diagonal artery (5 times), the marginal branch (67 times), the circumflex artery (7 times) and the right coronary artery (2 times). Seventy-five complementary saphenous vein bypasses were performed in 58 patients. Operative mortality was 2.5%. Two patients had perioperative myocardial infarcts (2.5%) on nonbypassed sites. Three patients had sternal wound infections (3.7%). Sixty-two patients (80%) were reexamined by angiography at month 6-25 in group 1 and 37 in group 2. Sixty left internal thoracic artery bypass grafts (97%) were patent versus 39 right internal thoracic artery bypass grafts (63%). In group 1, 23 of 25 left internal thoracic artery bypass grafts were patient (92%) versus 12 right internal thoracic artery grafts (48%). In group 2, all 37 left internal thoracic artery bypass grafts were patent (100%) versus 27 right internal thoracic artery grafts (73%). With this procedure, particular attention must be paid to the length of the right internal thoracic artery, and extensive training is required.