The authors report six cases of atrial septal defect (ASD) associated with abnormal drainage of the inferior vena cava into the left atrium responsible for right-to-left shunting, without pulmonary hypertension. The abnormal drainage could be due either to an anatomical malposition of the inferior vena cava opening into the left atrium, or to an abnormal blood flow from this vein, normally located through a low ASD, under the influence of anatomical, mechanical and haemodynamic factors. Clinically, all patients presented with light cyanosis and with the usual signs of ASD. None of them had elevated pulmonary pressure. The lesion, suggested by clinical findings, was diagnosed either at angiography, which in four cases demonstrated an abnormal pulmonary venous return, or at colour-coded doppler echocardiogram, or at surgery. In every case, surgical correction consisted of closure of the often low-sited ADS by a patch which diverted the inferior vena cava into the right atrium and the abnormal venous return towards the left atrium. The short--and long-term results of surgery were excellent. The authors review the literature concerning this unusual association of ASD with an abnormal drainage of the inferior vena cava into the left atrium.