Klebsiella pneumoniae is an opportunistic pathogen associated with nosocomial infections. Persister cells are a fraction of a bacterial population that can escape antibiotic treatment and are associated with antibiotic therapy failure. In this work, we analyzed persistent cells in planktonic cultures and biofilms using10 K. pneumoniae clinical isolates and four different antibiotic types. The isolates had different antibiotic susceptibility profiles that did not correlate with their capacity to form biofilms. Persister cells were found under all conditions tested, although their population numbers varied depending on the antibiotic used. A larger number of persister cells were found in biofilms than in planktonic cultures. Antibiotic treatment with trimethoprim-sulfamethoxazole resulted in the largest persister cell sub-population compared with other antibiotics tested, while ciprofloxacin was the antibiotic that produced fewer persister cells. These results indicate that K. pneumoniae clinical isolates vary not only in their susceptibility to antibiotics but also in properties relevant to diseases, such as biofilm formation and persister cell populations.