Clonality was tested in 86 tumours from 25 patients with recurrent and multifocal superficial bladder transitional cell carcinomas (TCCs) using the analysis of TP53 mutations and of LOH in the 17p13 and 9p21 regions. Tumours from the majority of individuals showed either absence or presence of the same TP53 mutation and/or an identical LOH pattern, with the same allele lost in all tumours. Only two pairs of tumours from two patients had discordant findings, which were incompatible with monoclonality. Therefore, our results rather support the monoclonal model of development of highly recurrent superficial bladder TCCs.