Hepatoblastoma, although rare, is the most common primary malignant neoplasm of the liver in children. In this paper we describe a case of hepatoblastoma with unusual cytologic features and present the histologic, immunocytochemical and ultrastructural features of this neoplasm. A 7-month-old girl presented with a large hepatic mass and metastatic nodules in both lungs. Intraoperative biopsy revealed a hepatoblastoma. Aspiration biopsy yielded a highly cellular aspirate with cords of pleomorphic cells embedded in a mucoid matrix. Histologic sections showed a diffusely infiltrative neoplasm composed of sheets and cords of highly pleomorphic cells. The neoplastic cells stained strongly positive for cytokeratin CAM 5.2 and AE1 and focally positive for alpha-fetoprotein, ferritin, carcinoembryonic antigen and vimentin. Ultrastructurally, the neoplastic cells had abundant intercellular junctions and intracytoplasmic aggregates of intermediate filaments. A mucoid matrix, to our knowledge, has not been reported as a finding on aspiration biopsy. This patient presented with pulmonary metastases, and thus we think the mucoid matrix may be a marker of a more aggressive variant of hepatoblastoma. This case illustrates additional cytologic features of hepatoblastoma and the usefulness of aspiration biopsy in the rapid diagnosis of this rare tumor.