Current recommendations for empirical therapy for community-acquired urinary tract infection (UTI) in women hinge on knowledge of antimicrobial susceptibility patterns in the geographic region of the practitioner. We conducted a survey of antimicrobial susceptibilities of 103,223 isolates recovered from urine samples that were obtained in 1998 from female outpatients nationally and within 9 geographic regions in the United States. Resistance of Escherichia coli isolates to trimethoprim-sulfamethoxazole varied significantly according to geographic region, ranging from a high of 22% in the western United States to a low of 10% in the Northeast (P<.001). There were no clinically significant age-related differences in the susceptibility of E. coli to any of the study drugs, but the susceptibility to fluoroquinolones of non-E. coli isolates that were recovered from women who were aged >50 years was significantly lower than that of isolates recovered from younger women (P<.001). The in vitro susceptibility of uropathogens in female outpatients varies according to age and geographic region.