Since 1985 we have performed arterial switch repair for infants with simple transposition of the great arteries (with intact or virtually intact ventricular septum) who were younger than 2 months of age. As of December 1990, a total of 118 arterial switch operations had been performed for transposition of the great arteries with intact ventricular septum. Although correction is usually performed in the first 14 days of life, 18 infants had operations at or after 21 days (range 21 to 118 days; mean 38 days). Fourteen of 18 patients had echocardiographic or catheter evidence (or both) of low left ventricular pressure at the time of operation. None of these patients had preliminary pulmonary artery banding. Mortality was 5.6% (1 of 18 patients, confidence limit 0.8% to 17%) for the older group versus 0% (0 of 100 patients; confidence limit, 0% to 1.8%) for patients less than 21 days of age. The single death occurred in a 22-day old, 1.8 kg premature baby, probably as a result of a problem with a coronary anastomosis. One patient required a left ventricular assist device for 2 days after the operation. These data suggest that with appropriate perioperative management and support, the arterial switch procedure can be safely carried out as a primary procedure for patients up to the age of 1 month and probably up to the age of 2 months.