We investigated clinical data and histological specimens of 46 patients with a hepatoblastoma (HB) for prognostic criteria. Disease-free survival (DFS) of 23 patients treated in the German Cooperative Study HB-89 (1988-1990) was 83%, in contrast to 40% in 10 children with other chemotherapy regimes (1977-1987) and 38% in 13 with only a tumour resection (P = 0.005). Tumour residence after resection (R category) correlated significantly with probability of DFS (P = 0.0001). This was also the case for pT status, according to the pTNM classification for liver carcinoma (P = 0.0007), involvement of one or both liver lobes (P = 0.004), multiplicity of tumour nodes (P = 0.001), vascular invasion (P = 0.0006) and expression of nucleolar organiser regions as an indicator for proliferation activity of tumour cells (P = 0.05). Patients' age and histopathological subtypes could only indicate outcome, while tumour size and serum alpha-fetoprotein values were not significantly related to prognosis. In multivariate analysis, pT status and R categories remained significant. These should be applied in all cooperative trials on HB.