Hepatoblastoma is the most common primary hepatic tumor in children, and only a limited number of detailed karyotypic analyses have been reported to date. In the present study, cytogenetic abnormalities were identified in nine cases of hepatoblastoma from a single institution. Among characteristic chromosomal changes detected were simple numerical aberrations, structural alterations of chromosomes 1, 2, and 8, and the recurrent unbalanced rearrangements der(4)t(1;4)(q25.2;q35.1) and der(6)t(1;6)(q21;q26). Array comparative genomic hybridization was applied in four of the cases. The combined cytogenetic, molecular cytogenetic, and histopathologic analyses are presented here, together with clinical data. The results substantially confirm previous findings of aberrations involving chromosomal loci on 1q, 2 or 2q, 4q, 6q, 8 or 8q, and 20 as significant in the development and clinical course of this disease.