From 1965 to 1980, 249 consecutive patients underwent a Mustard procedure for simple transposition of the great arteries. Hospital mortality was 23 of 249 (9.2%); follow-up for 24 years (mean, 11.7 +/- 6.1 yr) revealed 50 of 249 (20%) late deaths, of which seven were noncardiac, six were in the hospital, and 37 were sudden (27 patients with poor hemodynamics and 10 unexplained). Actuarial survival after 1, 10, and 20 years was 85, 75, and 67%. The instantaneous risk of death decreased rapidly after surgery but showed a second peak from 8 to 15 years postoperation. When last seen 87% were in New York Heart Association (NYHA) class I; 69% had sinus rhythm, 20% nodal rhythm, 10% atrial flutter, and 1% paced. Survival in uninterrupted sinus rhythm after 5, 10, and 20 years was 75, 62, and 47%. Nodal rhythm detected by annual ECG occurred in 69 patients. Excluding the early experience, the risk of loss of sinus rhythm was constant in time and constant throughout the experience (2.4%/yr). Atrial flutter was observed in 36 patients. Occurrence of atrial flutter was limited to two discrete surgical periods: the first operations (26 with atrial flutter of the first 50) and an ill-defined period in the middle of the experience. Patients not operated on during these two periods were very unlikely to develop atrial flutter (one of 104, p less than 0.001). As for death, the hazard function showed a bimodal curve, the second peak appearing earlier from 5 to 11 years. If nodal rhythm was noted on the yearly routine ECG, the risk for developing subsequent atrial flutter increased by a factor of 2.1 (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)