Inferences: A treatment protocol for patients with simple transposition, consisting of initial balloon atrial septostomy and leading to a delayed atrial switch repair of the Mustard type, in good circumstances, results in survivorship at 1 month, 1 year, 10 years, and 20 years of 95% (95% confidence limits [CL] 90% to 97%), 90% (95% CL 84% to 94%), 83% (95% CL 74% to 90%), and 80% (95% CL 70% to 88%), respectively. Low birth weight adversely affects survivorship. Hypoxia or heart failure accounts for most deaths within the first month and before the atrial switch (Mustard) repair. Most of the few deaths late postoperatively are sudden and they appear to occur particularly in patients who have junctional rhythm. A progressive increase in the prevalence of junctional rhythm has been a risk of the atrial switch repair, and only 76%, 65%, 59%, 56%, and 53% of patients can be expected to be free of this by 1, 5, 10, 15, and 20 years after repair. Important right ventricular dysfunction late after an atrial switch repair, with its adverse affect on the patients' functional capacity, appears to be present in up to 10% of patients after the atrial switch repair, but may not be an immutable risk of this type of repair. About 90% of patients, essentially all of those who do not have right ventricular dysfunction, can be expected to be in New York Heart Association class I or II late postoperatively.