The epidemiology of quinolone resistance and the concomitant resistance to other antibiotic classes was investigated in 445 Klebsiella pneumoniae and 238 Klebsiella oxytoca isolates. Decreased susceptibility to ciprofloxacin was found in 7.2% and 3.4% of these two species, respectively. Ciprofloxacin resistance was significantly linked to ceftazidime resistance, the hallmark of extended-spectrum beta-lactamase production, as well as to resistance to all antibiotic classes tested. Using automated ribotyping, seven intrahospital- and interhospital-transmitted clones of ciprofloxacin-resistant isolates were found. The newer fluoroquinolones sitafloxacin and clinafloxacin may become increasingly valuable, since they proved to be active also against ciprofloxacin-resistant isolates.