Wilms' tumour (WT) is the most common solid tumour of childhood. The molecular signalling pathways determining the origin and behaviour of WT are very complex and several genes in several loci may participate. This review tries to briefly compile recent works on the histology and on the molecular alterations that promote the genesis, development and behaviour of WT. Some molecular alterations seem to be associated with specific histological types and particular clinical outcomes, suggesting that they might be utilised to determine the prognosis and to identify poor prognostic subgroups that can be targeted for more individualised treatments.