A single kidney in patients with agenesis or after nephrectomy is regarded as a risk factor. Primarily, the role of glomerular hyperfiltration and later possible glomerular sclerosis are emphasised. Complex treatment of Wilms tumour patients includes previous chemotherapy and radiotherapy. The aim of our study was to investigate late sequelae of this aggressive treatment on the morphology and function of a single kidney and to compare these results with a group of single kidney patients, where the diagnosis of Wilms tumour was excluded.