A palliative operation to create intraatrial transposition of venous return without concomitant closure of an associated ventricular septal defect (palliative Mustard or Senning operation) has been used primarily for patients with a combination of transposition of the great arteries, ventricular septal defect, and pulmonary vascular obstructive disease. We evaluated the results in all 15 patients (median age 13 years) who had this procedure at the Mayo Clinic between 1973 and 1979. There were two (13%) operative deaths. One patient was lost to long-term follow-up. Of the 12 operative survivors for whom follow-up data were available, 11 reported subjective improvement in exercise tolerance and activity level. There were seven late deaths: six from cardiovascular problems and one from an accident. There are five survivors currently alive (average 10.8 years after operation). Patients who survived the operation for more than 5 years had a significantly (p less than 0.05) lower pulmonary resistance preoperatively than those who survived less than 5 years. The hemoglobin level decreased from 21.1 gm/dl before operation to 18.4 gm/dl, and arterial saturation was increased from 64% to 85% at an average of 9 years after operation. We conclude that this operation produces subjective improvement and lessens hypoxemia and polycythemia. In some patients, palliation may be achieved for 10 years or longer.