We collected 76 clinical isolates of Acinetobacter baumannii (amikacin MIC by Vitek 2 AST-N055 card: ≤2μg/mL, 11 isolates; 4μg/mL, 19 isolates; 8μg/ mL, 17 isolates; 16μg/mL, 27 isolates; and ≥64μg/ mL, 2 isolates) from a university hospital and evaluated the Vitek 2 AST-N055 card vs the broth microdilution as a reference method for testing susceptibility to amikacin. Vitek 2 AST-N055 card yielded very major errors in 15 isolates (19.7%) and minor errors in 26 isolates (34.2%). Of the 15 isolates shown very major errors, 14 had Vitek 2 MICs ranging from 8 to 16μg/mL. The results of our study suggest strongly that it is unreliable to test the amikacin susceptibility by Vitek 2 AST-N055 card of A. baumannii with the Vitek 2 MICs ranging from 8 to 16μg/mL. In those cases, another susceptibility test, such as broth microdilution (BMD), should be performed to confirm the results. (Korean J Clin Microbiol 2009;12:144-145)