A case of aorticopulmonary window associated with tetralogy of Fallot is reported with its clinical, hemodynamic, angiocardiographic, surgical, and necropsy findings. The difficulty in diagnosing a tetralogy of Fallot in the presence of a large aorticopulmonary shunt is emphasized. It is also noted that the only means of discovering the infundibular stenosis of the right ventricle is by angiocardiographic study of the right ventricular outflow tract. The difficulty in distinguishing truncus arteriosus from an aorticopulmonary window coexisting with a ventricular septal defect is discussed, and it is pointed out that the only means of differentiating these two anomalies is the angiocardiographic finding of two sigmoid valves. An embryological hypothesis concerning the pathogenesis of this association is also discussed.