During a 2-year period (April 2005–March 2007), 31 intensive care unit (ICU) patients in a Greek hospital were infected or colonised with imipenem-resistant isolates of Acinetobacter baumannii. Twelve patients died, with imipenem-resistant A. baumannii infection contributing to the death of seven patients. The 31 representative A. baumannii isolates were multidrug-resistant and clustered in four distinct clones, each of which contained different carbapenemase genes: clone I was predominant and contained blaVIM-1, blaOXA-58 and the intrinsic blaOXA-66 gene; clone II contained blaVIM-4, blaOXA-58 and the intrinsic blaOXA-69 gene; clone III contained blaOXA-58 and the intrinsic blaOXA-69 gene; and clone IV contained only the intrinsic blaOXA-66 gene. IS Aba1 was not associated with the intrinsic blaOXA-51-like alleles, whereas IS Aba3 was found upstream and downstream of blaOXA-58 in isolates of clone I, and upstream of blaOXA-58 in isolates of clone III, but was not detected in isolates of clone II. PCR, curing and hybridisation experiments indicated that the blaVIM alleles were chromosomally located, whereas the blaOXA-58 alleles were plasmid-located. This study provides the first description of the clonal spread of multidrug-resistant A. baumannii isolates carrying blaVIM-1 and blaVIM-4 metallo-β-lactamase genes, and revealed that distinct carbapenem-resistant A. baumannii clusters bearing different carbapenemase genes may emerge and cause severe infections, even in a well-defined regional hospital setting.