The majority of urinary tract infections are caused by strains of uropathogenic Escherichia coli. One of the characteristics of urinary tract infections is the high frequency of recurrence, usually caused by the same bacterial line causing the primary infection. The results of a recent study revealed that the reason for recurrent infection lies in residual bacteria that persist in latent form inside uroepithelial cells after the acute primary infection. In the endosomal vesi­cles of urothelial cells, uropathogenic Escherichia coli is thus protected from both the immune system and most antibiotics. It has also been found recently that uropathogenic Escherichia coli spends most of its lifetime inside terminally differentiated urothelial cells. The most impor­tant factors of successful proliferation of uropathogenic Escherichia coli were found to be the ultrastructural characteristics of these differentiated cells, such as the disappearance of actin filaments from the subapical region of urothelial cells. Uropathogenic Escherichia coli seems to exit urothelial cells only to be disseminated to other uninfected cells. The recent discovery of uropathogenic Escherichia coli as an intracellular parasite indicates new treatment modal­ities for recurrent cystitis.