OBJECTIVE To investigate the potential role of platelet-derived growth factor-AA (PDGF-AA) and the PDGF-alpha receptor as prognostic markers in Wilms' tumour. PATIENTS AND METHODS The expression of PDGF-AA and PDGF-alpha were investigated using immunohistochemical analysis of 62 Wilms' tumours. Patients were treated with chemotherapeutic agents before surgery and had a mean follow-up of 6.4 years. RESULTS PDGF-AA and PDGF-alpha were expressed by the mesenchymal tissue of the normal kidney and mainly detected in the epithelial component of Wilms' tumour. Immunoreactive tumour epithelium cells were found in 50% and 55% for PDGF-AA and PDGF-alpha, respectively. The epithelial expression of both PDGF-AA and PDGF-alpha correlated with pathological stage. Univariate analysis showed that epithelial PDGF-AA and PDGF-alpha receptor expression were indicative of clinical progression. In a multivariate analysis, PDGF-alpha protein expression by epithelial cells was an independent prognostic marker of a favourable prognosis. CONCLUSIONS Expression of both PDGF-AA and PDGF-alpha in the epithelial part of Wilms' tumour correlated with tumour stage and clinical progression. Our data suggest that both PDGF-AA and PDGF-alpha receptor expression are related to prognosis.