Due to the lack of uniformity in the criteria for formulating the diagnosis of the syndrome of heterotaxy, 12 cases with this abnormality were reviewed. The patients were selected on the following basis: symmetrical liver, changeable P waves in consecutive electrocardiograms, bronchial isomerism, hematological disturbances, anomalous relationship of the inferior vena cava and abdominal aorta, anomalous systemic and pulmonary venous drainage and complex cardiac malformations. The most frequent findings were: symmetrical liver, changeable P waves, anomalous systemic venous return, anomalies of the atrio-ventricular valves, particularly atrioventricular canal, aorto-cava juxtaposition, single atrium, anomalous pulmonary venous return, transposition of the great arteries and pulmonary stenosis. Less frequent anomalies were: atrial and ventricular septal defects, atrial isomerism, truncus arteriosus and partial distortion of the great arteries. The hematological disturbances as well as the radioisotope scanning of the liver and the spleen were of little help. Suggestions are given for the diagnosis of the syndrome and for the evaluation of present diagnostic procedures making necessary to use the data gathered with more precision.