In recent years there have been initiatives to revise nomenclature of urothelial tumours of the bladder. In 2004 The World Health Organisation published nomenclature of tumours, in which the biologic nature of tumours as well as verifiable cytogenetic and molecular biologic changes, were taken into account. In the new 2004 WHO classification there are two large opposing groups of tumours: non-invasive and invasive. Authors of the new classification have agreed that there are two subtypes of urothelial tumours that have visibly different clinical route (progression). On one side there are genetically stable tumours that include non-invasive papillary urothelial neoplasm of low malignant potential and urothelial low grade carcinoma. On the other side there are genetically unstable tumours with non-invasive and invasive high grade carcinoma. In this paper the new histological 2004 WHO classification is described.