A meta-analysis of six double-blinded clinical trials was undertaken to identify risk factors associated with bacteriologic outcome in 3,108 women with acute cystitis. Eleven antibiotic regimens were used, including ciprofloxacin, ofloxacin, norfloxacin, trimethoprim-sulfamethoxazole, and nitrofurantoin. Entry criteria for all studies were identical. Among 2,409 patients who were defined to be valid for efficacy analysis, pathogens included Escherichia coli (78.6%), Staphylococcus saprophyticus (4.4%), Klebsiella pneumoniae (4.3%), Proteus mirabilis (3.7%), and "other" (9%). Causative bacteria were eradicated at the end of treatment in 93% of patients. The following parameters were associated with successful bacteriologic outcome: not using a diaphragm (P = .0041), treatment for > or = 3 days (P = .0043), pathogen not "other" (P = .0043), symptom duration of < 2 days (P = .0096), and African American race (P = .0147). K. pneumoniae (P = .0496) and "other" pathogens (P = .0018) were associated with increased probability of bacteriologic treatment failure. The presence of pyuria (> or = 10 WBCs per high-power field) did not correlate with outcome and was inversely correlated with the finding of > or = 10(5) bacterial colony-forming units per mL of urine (P < .001). This large database identifies new parameters associated with treatment outcomes of acute cystitis and calls into question current clinical trial guidelines.