Paradoxical septal motion is considered to be a characteristic feature of total anomalous pulmonary venous drainage, reflecting the right ventricular volume overload in this condition. Patients with additional pulmonary venous obstruction have reduced pulmonary blood flow, and would be expected to show normal septal motion. We have studied the haemodynamic and echocardiographic findings in 21 patients with proven total anomalous pulmonary venous drainage and found paradoxical septal motion in only 11 instances. Paradoxical septal motion was present in all nine patients over the age of 1 month. Of the 12 neonates, 10 showed normal septal motion. Patients with normal septal motion had clinical features of pulmonary venous obstruction, with significantly higher pulmonary artery pressures and lower pulmonary artery saturations than patients with paradoxical septal motion. It is concluded that in total anomalous pulmonary venous drainage, septal motion reflects pulmonary blood flow, allowing separation of patients into those with or those without pulmonary venous obstruction.