Since the use of fluoroquinolone antibiotic in clinical practice was introduced about a decade ago, quinolone-resistant E. coli (QREC) strains are being isolated with increasing frequency. From 1996 to 2000, 297 cases of urinary tract infection (UTI) due to QREC were observed in our hospital; 218 episodes (73.5%) were community acquired. The incidence of QREC UTIs increased steadily from 14.4% to 21.3% during 5 years when we compared the clinical characteristics of 60 QREC UTI with those of 80 quinolone-susceptible E. coli UTIs. Significant differences in susceptibility to various antibiotics were observed between the QREC and QSEC strains of E. coli. The multidrug resistance rate of QREC was much higher (38.3%) than those of quinolone susceptible isolates (18.8%). Prior fluoroquinolone use (p = 0.05), old age (p = 0.001), and a vegetative state (p = 0.03) were the independent risk factors for the acquisition of QREC UTI. The outcome of E. coli UTI is dependent on quinolone resistance. Thirty-day mortality was higher in QREC UTI patients, probably due to aggravation of underlying illness, but not quinolone resistance. On the basis of PFGE analysis, although some clustering was found in the hospital, genomic diversity was found among both the community and nosocomial strains. The increased frequency of QREC UTIs is thus not due to transmission of resistant strains but probably results from the selection of resistant strains from the endogenous flora of patients.