BACKGROUND: Wilms' tumour (WT) is the most common solid tumour affecting young children. Its histological diversity leads to difficulties in predicting the outcome. MATERIALS AND METHODS: Image analysis cytometry and immunohistochemistry with a selected panel of antibodies were performed in 23 cases of WT considered of intermediate risk according to the revised International Society of Pediatric Oncology (SIOP) working classification of renal tumours of childhood. In this series, a tumour was considered aggressive according to its propensity for metastases or its recurrence. RESULTS: Out of the 14 non-aggressive WT, 4 were found to be diploid and 10 were aneuploid including 6 that were heterogeneous for DNA-ploidy. All the tumours presented a low proliferative index and were negative for p53 and p57(kip2) immunostaining. Out of the 9 aggressive tumours, all were aneuploid and 4 were found to be heterogeneous for DNA-ploidy. They all presented a high degree of cell proliferation and 7 were positive for p53 immunostaining. Only two were positive for the p57(kip2) marker. The only fatal case revealed an aneuploid-homogeneous DNA-ploidy analysis, was p53 and p57(kip2) positive and presented a high cell proliferation index. CONCLUSION: A significant correlation between the presence of focal DNA-aneuploidy in Wilms' tumours and adverse prognosis is not established, but some immunohistochemical markers may be useful for the clinical evaluation of these tumours and to help in predicting the risk of an unfavourable outcome.