Over a 10-year period, 123 patients with transposition of the great vessels underwent the Mustard procedure. The hospital mortality for the series was 10.6%. There were seven late deaths, five of which were presumable due to arrhythmia. Sinus rhythm was noted postoperatively in 53% of the patients. Almost all the survivors had achieved catch-up growth when evaluated 6 months to 10 years later. A growth spurt was more consistently seen in the patients who were operated on under 2 years of age. Physical endurance and school performance were on a par with their normal peers or better in about half of the survivors. Severe neurologic problems were present in five patients. Postoperative catheterizations in 42 patients showed a rather high incidence of residual interatrial shunts, mild left ventricular outflow obstruction, and mild superior vena caval obstruction. Pulmonary venous obstruction and serious tricuspid regurgitation were not encountered.