Renal tumours of childhood represent a fascinating group of tumours in which very significant discoveries have been made in the last 100 years, leading to better understanding of these not only tumours but also tumour in general. By studying a large series of renal tumours of childhood collected through international multicentre trials, their clinico-pathological features have been better recognised resulting in more appropriate treatment and better prognosis, numerous new tumour entities have been identified, and thank to new molecular biology studies and techniques, many tumour genes and genetic abnormalities which are important in tumorigenesis have been found. The most common renal tumour of childhood is Wilms' tumour, which is now regarded as the most treatable tumour in children with overall survival of 90%. New multicentre trials are focused on reduction of treatment in order to avoid long-term sequalae of treatment, but without jeopardising these excellent survival results. Histopathological studies are searching for subtypes of Wilms' tumour, which could be treated with milder therapy, and in a recently launched trial patients will be stratified in different treatment groups on the basis of molecular features of their tumours. Molecular biology studies have helped us recognising that some renal tumours are identical to tumours of other sites (such as cellular mesoblastic nephroma and infantile fibrosarcoma of soft tissue, renal and extra-renal rhabdoid tumour), as well as that some tumours of other sites may also occur in the kidney (primitive neuroectodermal tumour, desmoplastic small round cell tumour, synovial sarcoma). Finally, some new, kidney-specific entities have been recognised too (metanephric stromal tumour, metanephric adenofibroma, anaplastic sarcoma of the kidney). It is very likely that new advances in molecular biology will result in identification of features, which are going to be even more important in predicting tumour behaviour, response to treatment and prognosis.