One hundred and thirty-eight isolates of Klebsiella pneumoniae showing resistance to ceftazidime were isolated from different wards of the Hospital de Santa Maria, Lisbon. The genomic DNA of the isolates was analysed by pulsed-field gel electrophoresis (PFGE) and two patterns were predominant. In all isolates the presence of a single large plasmid of about 50 kb suggested that propagation of the outbreak prominently involved plasmid spread. The deduced amino acid sequence indicated the presence of a TEM-10 beta-lactamase. This extended-spectrum beta-lactamase was present among K. pneumoniae isolates, was widely disseminated in different wards and remained persistent as a result of an outbreak involving the dissemination of both the multi-resistance plasmids harbouring the bla gene and the isolates themselves.