Asymptomatic bacteriuria is common in the elderly, occurring in as many as 25-50% of elderly nursing home residents. Asymptomatic bacteriuria itself should not be treated with antimicrobial therapy. Difficulties in communication, chronic genitourinary symptoms, and the high frequency of positive urine cultures, make ascertainment of symptomatic infection problematic for the functionally impaired elderly. Chronic genitourinary symptoms are not a manifestation of acute urinary infection, although acute deterioration in symptoms may be consistent with infection. Fever in an institutionalized elderly subject with a positive urine culture and without an indwelling catheter is due to urinary infection in less than 10% of episodes. However, there are no criteria to differentiate urinary infection from other sites in this clinical scenario. Thus, neither urine culture nor clinical presentation allows a diagnosis of symptomatic urinary infection to be made with a high level of certainty. Decisions with respect to antimicrobial therapy must be made on an individual basis and with an understanding of these diagnostic limitations. It is not realistic to expect to optimize antimicrobial usage in this population until issues of diagnostic uncertainty are addressed.