Transposition of the great arteries (TGA) is a common malformation which sometimes has a dramatic presentation at birth but which is completely curable with early and appropriate initial management. Antenatal diagnosis of this condition may change the neonatal prognosis. The authors compared morbidity and mortality in the pre- and postoperative periods of 68 neonates with an antenatal diagnosis of TGA (foetal diagnosis) with that of 250 neonates in whom the diagnosis was made after birth (neonatal diagnosis). The delay before admission to the department was 2 +/- 2.8 hours in the foetal group and 73 +/- 210 hours in the neonatal group (p < 0.01). Severe haemodynamic distress (metabolic acidosis, multi-organ failure) were more common in the neonatal group (p < 0.01). Management on admission was identical in the two groups (p > 0.05). The preoperative mortality was 15/250 in the neonatal group (6%, 95% CI = 3-9%) compared with 0/68 in the foetal group (p < 0.05). The postoperative morbidity was comparable in the two groups (25/235 and 6/68) but the hospital stay was longer in the neonatal group (30 +/- 17 versus 24 +/- 11 days, p < 0.01). Finally, postoperative mortality was significantly higher in the neonatal group (20/235 compared with 0/68, p < 0.01) although the risk factors of death at arterial switch surgery were identical in the two groups. Therefore, antenatal diagnosis of TGA reduces neonatal morbidity and mortality in this condition. Antenatal diagnosis must be developed by the education of obstetricians. The transfer of mothers with a foetus affected by TGA to centres capable of assuming the initial management, sometimes during labour, is essential.