Ninety children with complete atrioventricular canal without any significant associated abnormality underwent surgery between 1973 and 1982. The first group of 26 infants, including 7 with trisomy 21 (average age 5.3 +/- 3.8 months) had severe pulmonary hypertension and underwent pulmonary artery banding: 10 died in the immediate or early postoperative period (38 p. 100). The mortality was 50 p. 100 in children under 6 months of age. In two cases, the banding was a failure because it was ineffective or "vicious" and both patients had to undergo reoperation 2 to 6 months later for total correction which resulted in 1 death and 1 poor result; the surviving 14 patients were improved: 3 are waiting for total correction under good conditions and 11 underwent open heart surgery 36 +/- 16 months after banding with 7 good results and 4 average results because of residual significant mitral regurgitation associated in one case with atrioventricular block requiring pacing. The overall results of this group were 42 p. 100 mortality, 19 p. 100 average results and 27 p. 100 good results; 12 p. 100 are waiting for surgery. The second group included 64 children, with 34 with trisomy 21 (average age 17.4 +/- 16.7 months) who underwent complete correction straight away (before 2 years in 50 cases, before 1 year in 30 cases). The operative mortality was 28 p. 100, but only 7 p. 100 in the 15 cases in which pulmonary atrial pressure did not exceed 2/3 of the systemic pressure and 35 p. 100 in the other 49 cases with severe pulmonary hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)