Urinary tract infections constitute a major cause of morbidity in women of childbearing age and represent the primary cause of nosocomial infections. The most common etiologic organism for urinary tract infections of all types isEscherichia coli. There has been a significant research effort over the last decade to understand whichE. colivirulence factors contribute to disease. The pathogenesis of urinary tract infections involves a complex interaction between the human host and bacteria. The sequence of events includes bacterial adherence and colonization of the uromucosal surface, proliferation, and induction of tissue injury or inflammation. Recent efforts to understand the uropathogenic process have included the following studies: epidemiology of adhesins, the role of adhesins, iron acquisition, urease production, host receptor status, and factors associated with inflammation. These topics are the subject of this review.