Pathogenicity of urinary tract infection (UTI) has been reviewed mainly focussing on the bacterial adherence in uropathogens and the inflammatory responses of urinary mucosa. Bacterial fimbriae or pili, which are encoded by chromosomal gene clusters played a major role in the adherence mechanisms of uropathogenic bacteria, including Escherichia coli. Furthermore, inflammatory responses in urinary mucosa including cytokine release was also investigated. The latest information concerning pathogenicity of UTI is described and discussed here.