We have investigated the molecular epidemiology and distribution of carbapenemase genes in 492 imipenem-non-susceptible Acinetobacter baumannii worldwide isolates (North and Latin America, Europe, Asia, South Africa and Australia). MICs were determined by broth microdilution and Etest. The presence of carbapenemase-encoding genes was investigated by PCR. Molecular epidemiology was performed by repetitive sequence-based PCR (rep-PCR; DiversiLab), sequence-type multiplex PCR and PFGE. Imipenem non-susceptibility was associated with ISAba1 upstream of the intrinsic bla(OXA-51-like) or the acquired carbapenemase bla(OXA-23-like), bla(OXA-40-like) or bla(OXA-58-like). Isolates were grouped into eight distinct clusters including European clones I, II and III. European clone II was the largest (246 isolates) and most widespread group (USA, pan-Europe, Israel, Asia, Australia and South Africa). The global dissemination of eight carbapenem-resistant lineages illustrates the success this organism has had in epidemic spread. The acquired OXA enzymes are widely distributed but are not the sole carbapenem resistance determinant in A. baumannii.