Mesenchymal hamartomas of the liver usually present within the first 2 years of life. Abdominal enlargement and respiratory distress are the most common presenting features. Pathologically, the lesion is composed of large cysts separated by septations. Review of sonograms and CT scans in nine patients shows that a large, predominantly cystic mass with internal septae is characteristic of the tumor. Angiography shows peripheral hypervascularity with a septated avascular center. A confident preoperative diagnosis of mesenchymal hamartoma based on these features is possible.