Genotypic diversity, antimicrobial susceptibilty, and presence of OXA-genes were assessed in 100 nosocomial Acinetobacter strains from a tertiary-care hospital, Turkey. Ninety-eight isolates were identified by AFLP library identification to Acinetobacter baumannii. Furthermore, the isolates were divided into 30 AFLP clusters and single strains at a similarity cut-off level of 90%, the defined strain level. Most of these clusters grouped together in larger clusters at a lower similarity level, indicating diversification beyond the strain level. At a similarity level of 80%, the A. baumannii isolates were allocated to eight clusters of multiple isolates (A, C, D, E, G, H, J, L) and 3 single isolates (B, F, I). Comparison of the isolates to those of the Leiden AFLP database revealed that the large cluster H (41 isolates) corresponded to a tentative novel international clone previously identified both by AFLP and MIST (CC15). Clusters D and E grouped with European (EU) clone II isolates, and cluster J with those EU clone I. Clusters A, C, G, and L could not be identified to any international clone. MLST of selected isolates of the major clusters corroborated the clone allocation by AFLP, except for the tested cluster A isolate which was identified to CC2 (EU clone II). Carbapenem resistance of 75 A. baumannii isolates was associated with the bla(OXA-58-like) gene or bla(OXA-51-like) with ISAba1 upstream. Altogether, 99% of the Acinetobacter isolates were multidrug resistant (MDR) and 77% extensively drug resistant (XDR). The findings show that multiple strains and clones MDR and XDR A. baumannii were endemic in the hospital. (C) 2012 Elsevier B.V. All rights reserved.