Overall survival after Mustard's operation was assessed in 130 patients with complete transposition of the great arteries and an intact ventricular septum who were operated on at the Brompton Hospital in the 12 year period from January 1974 to December 1985. Actuarial analysis showed a survival at five years of 79.1% (25 deaths in 130 patients). Half the deaths occurred within a month of operation and half up to five years later. Operation under the age of three months carried a greater mortality (six deaths in 11 patients). Statistical analysis showed that these survival figures were consistent throughout the series and did not alter with the year of operation. In the light of recent trends in treatment of this lesion, it is concluded that for neonates an arterial switch procedure is now likely to carry the best chance of long term success. For the patient who presents after the age of three months, however, there may still be a place for the Mustard procedure.