Proteus mirabilis expresses different types of fimbriae simultaneously. Several fimbrial types have been described and their role in the colonization of the urinary tract is under study. Previously, P. mirabilis fimbriae (PMF) have been shown to be associated with bacterial colonization of the lower urinary tract but not of the kidneys. In this study, a pmfA mutant was generated and used in several in vivo and in vitro studies. Two different urinary tract infection models in the mouse and two in vitro assays of bacterial adhesion to uroepithelial cells were performed. Expression of PmfA in a collection of P. mirabilis strains of different sources was also assessed. The results shown here indicate that PMF are involved in both bladder and kidney colonization by P. mirabilis and that these fimbriae are widely distributed among P. mirabilis isolates from different origins since all strains tested expressed PmfA.