Twenty patients with visceroatrial situs abnormalities were examined by sonography or computed tomography (CT). Eighteen patients underwent cardiac catheterization. Left isomerism (polysplenia syndrome) was found in seven patients, right isomerism (asplenia syndrome) in eight, and total situs inversus in five. The abdominal features of polysplenia include interruption of the inferior vena cava with azygous/hemiazygous continuation (100%) and multiple splenules. The diagnostic signs of asplenia include an inferior vena cava and aorta that course together on the same side of the spine with inferior vena cava-atrial communication (100%). In each case, the key differential feature relates to the major abdominal vessels. Sonography or CT examination in cases of situs ambiguus may reveal diagnostic features that can be used with radiographic signs to accurately diagnose the visceroatrial situs.