Clinical and morphological findings in 91 patients with infantile hemangioendothelioma of the liver are reported. The study comprised 56 girls and 35 boys ranging in age from premature infant to 3 yr; one outlier patient was 18 yr old. Most patients with infantile hemangioendothelioma (87%) were first seen before the age of 6 mo. Congestive heart failure was evident in 15%. Skin hemangiomas were noted in 11%. Anemia, hyperbilirubinemia and increased AST level were present. Solitary lesions were more common than multiple ones (3:2). Immunohistochemical staining of tumor cells for factor VIII was positive in 20 of 21 cases tested; testing for blood group antigen was positive in 8 of 28 cases. Cytokeratin staining verified the presence of bile ducts, some of which appeared to be the result of transformation of injured liver. No pericytes were identified on electron microscopy. The 6-mo survival rate, based on 71 cases, was 70%. Average time of follow-up for the survivors was 7.7 yr. All deaths occurred during the initial presentation/hospitalization of infants, with the exception of two patients who died 3 mo and 7 mo after diagnosis. More recent analytic methods, including immunohistochemical stains and flow cytometric studies, do not contribute to the practical assessment of this tumor. Covariates with significant value in predicting death 6 mo after diagnosis included presence of congestive heart failure, jaundice, multiple tumor nodules and absence of cavernous differentiation. (Hepatology 1994;20:39–45.)