Mortality before surgery must be taken into account when comparing the surgical mortality of atrial redirection procedures (Mustard's or Senning's operation) and the arterial switch operation for patients with complete transposition. This is because the switch operation is usually performed within the neonatal period or early infancy but Mustard's or Senning's operation usually after 4 months of age. The outcome of balloon atrial septostomy was therefore assessed in all 102 infants with transposition of the great arteries (plus or minus associated anomalies) who underwent the procedure at our hospital in the 10 years from January 1975 to December 1984. We considered the procedure to have been unsuccessful if the patient died from any cause (including other surgical procedures) between the septostomy and subsequent interatrial repair (Mustard's operation) or arterial switch operation. Eighteen patients died, although in only two was this as a direct result of the septostomy. Statistical analysis showed that low weight, presence of a persistent arterial duct, and coarctation of the aorta were significant risk factors. Early survival of infants with transposition of the great arteries has been dramatically improved after the introduction of balloon atrial septostomy.1-3 Nevertheless, there is considerable attrition before definitive repair, which must be included in the prediction of overall outcome.4-1.