Abstract It is common practice to define, as a different genotype, bacteria with unequal antibiotic susceptibility phenotypes. Here, we describe the utility of this practice for Acinetobacter baumannii. We determined antibiotic susceptibility for 19 clinical isolates of A. baumannii. REP-PCR was used to determine genotypes. Although all isolates were of the same genotype, 79% were predicted to be different based on susceptibility patterns. The antibiotic susceptibility phenotype does not accurately predict the genotype of A. baumannii.