In spite of an adequate balloon atrial septostomy, some neonates (less than 28 days of age) with transposition of the great arteries and intact ventricular septum (TGA, IVS) remain hypoxemic and acidotic and require operative treatment. Our entire experience with the Senning operation in neonates with TGA, IVS is reviewed. From March 1978 to March 1983 there were 104 infants who underwent the Senning operation for TGA, IVS. Of these, 19 were neonates (18%). The mean age at operation was 12 days (2 to 24) and mean weight was 3.52 kg (3 to 4.38). Two died early (10%) and one died late (5%). The last 16 are alive and well. Causes of early mortality were sepsis and severe obstruction of the superior vena cava. The cause of late mortality was severe pulmonary venous obstruction. Among the 16 survivors, postoperative courses, both early and late, have been remarkably benign. Ten patients have undergone postoperative cardiac catheterization (mean follow up 17 months). Two (12%) had severe pulmonary venous obstruction (one diagnosed by two-dimensional echocardiography), but both were successfully repaired. Atrial shunt was noted in two patients (12%), one of which underwent elective repair. Five infants have dynamic subvalvular pulmonary stenosis of various gradients (9 to 93 mm Hg). One infant has mild tricuspid regurgitation. There are no cases of superior vena caval obstruction or right ventricular dysfunction. Twenty-four hour electrocardiographic monitoring (mean follow-up 25 months) showed predominant normal sinus rhythm in 15 infants and predominant junctional rhythm in one.(ABSTRACT TRUNCATED AT 250 WORDS)