Mesenchymal hamartoma of the liver is the third most common liver tumor of infancy. The lesion is primarily mesenchymal in origin, believed to arise from a developmental abnormality in the formation of ductal plates during late embryogenesis. Several studies have revealed a recurrent translocation in mesenchymal hamartomas, all involving a breakpoint at chromosome band 19q13.4. We present a case with a deletion involving this locus. A 10-month-old girl presented with an asymptomatic abdominal mass. The 21.0-cm tumor arose from the surface of the liver. The cut surfaces displayed multiple cysts with intervening loose fibrous tissue. Microscopically, the tumor was mostly composed of edematous connective tissue with intervening cysts, islands of hepatocytes, and haphazard branching bile ducts. Cytogenetic analysis revealed an interstitial deletion on the long arm of chromosome 19(q13.1q13.4). The patient was discharged on postoperative day 4 without complications. The cytogenetic findings support the involvement of an alteration of a gene at chromosome band 19q13.4 in the pathogenesis of mesenchymal hamartoma of the liver.