An ecological approach to the pathogenesis of uncomplicated urinary tract infections allows awareness of the continual battle being waged in the vagina, urethra, and bladder between the bacterial invaders and the host defense mechanisms. Despite overwhelming odds, the bacteria must be able to persist, colonize, and finally adhere to these various battlefields on their ascent to the bladder itself. The large number of patients presenting to physician offices with acute simple cystitis attests to the fact that the bacteria occasionally win the battle of the bladder. An understanding of the pathophysiology of this constantly raging battle may help us modify our clinical approach to women with simple uncomplicated urinary tract infections.