Objective : To evaluate the accuracy of prenatal diagnosis with ultrasonography in cardiosplenic syndromes and to determine the spectrum of cardiovascular and other associated anomalies, and outcome. Methods : This was a retrospective survey of prenatal ultrasonography suspected as cadiosplenic syndrome in the investigators��� institution over a 10- year period through 1998. Results : In 25 of 56 fetuses the prenatal diagnosis of cardiosplenic syndromes was confirmed postpartum by echocardiography or autopsy records. Among 25 fetuses, 7 had left isomerism and 16 had right isomerism on postnatal evaluation. Most major intracardiac lesions, the pulmonary venous connections, superior and inferior vena caval anatomy were correctely diagnosed in utero (100%, 92%, 66%, and 87% accuracy, respectively). Right isomerism more than left isomerism was associated with atrioventricular septal defect (83% versus 31% ; P< 0.005), pulmonary outflow obstruction (50% versus 10% ; P<0.005), total anomalous pulmonary venous drainage (66% versus 10% P<0.005), whereas inferior vena cava interruption (0% versus 95% ; P<0.005), bradyarrhythmia (0% versus 26% ; P<0.005) were less common. Survival of managed children with left isomerism was better than for those with right isomerism (P<0.05). Conclusion : Fetal cardiosplenic syndromes can be diagnosed with high accuracy by prenatal ultrasonography. Left isomerism should be suggested in the presence of interruption of inferior vena cava with azygos continuation, fetal bradyarrhythmia, polysplenia, and structural heart disease. Right isomerism should be suspected in the presence of structural heart disease, namely atrioventricular septal defect, anomalous pulmonary venous connection, and asplenia. Prognosis of right isomerism was worse compared with left isomerism because of more complex associated cardiac defects and the inability to perform successful surgical procedures.