BACKGROUND AND PURPOSE Increasing rates of fluoroquinolone resistance among Escherichia coli have been reported in Taiwan and worldwide. We aimed to identify the risk factors of ciprofloxacin resistance in urinary E. coli isolates. METHODS Patients with positive urine culture result for E. coli and resistance to ciprofloxacin between September 1, 1999 and December 31, 1999 were prospectively identified as cases, and compared with ciprofloxacin-susceptible E. coli isolates (controls). THE CASE control ratio was 1:2. Data were collected with standardized case record forms. RESULTS Sixty one cases and 122 controls were compared. Multivariate analysis indicated that urinary tract catheterization (odds ratio [OR] = 2.631, 95% confidence interval [CI] = 1.058-6.544; p=0.037) and prior exposure to quinolones (OR = 13.072, 95% CI = 3.367-50.75; p<0.001) were independent risk factors for ciprofloxacin resistance in urinary E. coli isolates. Compared with ciprofloxacin-susceptible E. coli isolates, ciprofloxacin-resistant E. coli isolates from urine specimens had a significantly higher rate of resistance to all other tested antimicrobial agents, except amikacin and imipenem. CONCLUSION In patients with urinary tract infection, urinary catheterization and prior quinolone exposure are associated with a high risk of ciprofloxacin-resistant E. coli which may cause treatment failure.