Levofloxacin is an antibacterial agent used for the treatment of a many types of acute infections in adults. This is a randomized, double-blind study of the safety and effectiveness of levofloxacin compared with ciprofloxacin in the treatment of adults with a complicated urinary tract infection. Complicated urinary tract infections include those associated with fever, chills, kidney involvement or anatomic and functional abnormalities of the bladder. Patients in one group are treated with 250 mg of levofloxacin taken once daily for 10 days, and the other group is treated with 500 mg of ciprofloxacin, also an antibacterial agent, taken twice daily for 10 days. Patients are followed for 5 to 9 days after completion of treatment (post-therapy) to assess clinical signs and symptoms of infection. Long-term follow up (4 to 6 weeks after the end of treatment) of those patients who respond to therapy provides further evaluation of clinical signs and symptoms. The primary assessments of effectiveness include the microbiological response (the eradication at post-therapy of the infectious organism identified at the start of the study) and the clinical response (the resolution of signs and symptoms at post-therapy compared with those at the start of the study). An additional assessment of efficacy includes the overall clinical response, which is described as cured, improved, or failed. Safety assessments include the incidence of adverse events throughout the study, clinical laboratory tests (hematology, serum chemistry, and urinalysis) and physical examinations at the start of the study and post-therapy. The study hypothesis is that levofloxacin is at least as effective therapeutically and as well tolerated as ciprofloxacin in the treatment of adults with complicated urinary tract infections. Two levofloxacin 125 mg tablets taken orally once daily (and two placebo tablets taken once daily, 12 hours later) for 10 days; or one ciprofloxacin 500 mg tablet and one placebo tablet taken orally twice daily for 10 days.