The ARESC (Antimicrobial Resistance Epidemiological Survey on Cystitis) study is an international survey to investigate the prevalence and susceptibility of pathogens causing cystitis. Female patients (n=4264) aged 18-65 years with symptoms of uncomplicated cystitis were consecutively enrolled in nine European countries as well as Brazil during 2003-2006. Pathogens were identified and their susceptibility to nine antimicrobials was determined. Escherichia coli accounted for 76.7% of isolates. Among E. coli, 10.3% of the isolates were resistant to at last three different classes of antimicrobial agents. Resistance was most common to ampicillin (48.3%), trimethoprim/sulfamethoxazole (29.4%) and nalidixic acid (18.6%). Fosfomycin, mecillinam and nitrofurantoin were the most active drugs (98.1%, 95.8% and 95.2% susceptible strains, respectively) followed by ciprofloxacin, amoxicillin/clavulanic acid and cefuroxime (91.7%, 82.5% and 82.4%, respectively). Resistance to ciprofloxacin was >10% in Brazil, Spain, Italy and Russia. Overall, Proteus mirabilis were more susceptible to beta-lactams and less susceptible to non-beta-lactams than E. coli, whereas Klebsiella pneumoniae strains, which are intrinsically resistant to ampicillin, were less susceptible to mecillinam (88.8%), fosfomycin (87.9%), cefuroxime (78.6%) and nitrofurantoin (17.7%). Resistance was rare in Staphylococcus saprophyticus, with the exception of ampicillin (36.4%) and trimethoprim/sulfamethoxazole (10.2%). In Italy, Spain, Brazil and Russia, the countries most affected by antimicrobial resistance, extended-spectrum beta-lactamase (ESBL) enzymes (mainly CTX-M type) were detected in 48 strains (39 E. coli, 6 K. pneumoniae and 3 P. mirabilis). Despite wide intercountry variability in bacterial susceptibility rates to the other antimicrobials tested, fosfomycin and mecillinam have preserved their in vitro activity in all countries investigated against the most common uropathogens.