OBJECTIVES: To compare the efficacy and safety of ciprofloxacin (CIP) oral suspension to trimethoprim/sulfamethoxazole (TMP/SMX) oral suspension among older women with acute urinary tract infections (UTIs). DESIGN: Prospective, randomized, open-label, multicenter study of older women (age 65 and older). SETTING: Community and nursing home. PARTICIPANTS: A total of 261 older women were evaluable for safety. Of these, 172 (86 community, 86 nursing home) were evaluable for clinical and bacteriological efficacy. INTERVENTION: Patients were randomized to a 10-day regimen of either CIP (250 mg/5 mL twice daily) or TMP/SMX (160/800 mg/20 mL twice daily). MEASUREMENTS: Clinical response 4 to 10 days posttherapy. RESULTS: For the efficacy-valid population, posttherapy clinical resolution was statistically superior following CIP (97%) versus TMP/SMX (85%) (95% CI=2.0-21.3; P= .009). Eradication of pretreatment bacterial isolates posttherapy was also higher following CIP (95%) versus TMP/SMX (84%) (95% CI=2.7-21.3; P= .019). For the intent-to-treat population, posttherapy clinical resolution was significantly higher in the CIP group (96%) than in the TMP/SMX group (87%) (95% CI=0.2-16.7; P= .025). Safety was assessed in the intent-to-treat population and the incidence of drug-related adverse events were significantly lower following CIP (17%) than following TMP/SMX (27%) (P= .047). Premature discontinuation due to these events was also less prevalent with CIP than with TMP/SMX (2% vs 11%, respectively) (P= .004). CONCLUSION: CIP suspension showed higher clinical success and bacteriological eradication rates than did TMP/SMX for both community-based and nursing home-residing older women with acute UTIs. Furthermore, CIP suspension was associated with significantly lower rates of adverse events and premature discontinuations compared with TMP/SMX suspension.