A descriptive retrospective analysis of 811 antibiograms in dogs and cats was carried out in orderto get a better insight into the prevalence of antimicrobial resistance against ‘critically important antimicrobialswith highest priority for human medicine’ in dogs and cats. A veterinary diagnostic laboratoryperformed antimicrobial susceptibility testing on 811 Escherichia coli isolates obtained fromveterinary clinical samples from dogs and cats in Flanders, Belgium. These isolates were mainly fromfecal (62.5%) or urogenital (30.5%) origin. A disk diffusion method with breakpoints provided by thesupplier of the antibiotic disks was used for antimicrobial susceptibility testing. The results indicatedthat 9.5% of the Escherichia coli isolates were resistant against or intermediate susceptible to marbofloxacine,16.7% to enrofloxacine and 15.7% to cefovecin. The unexpected difference in resistancebetween marbofloxacine and enrofloxacin may be, at least partially, explained by the different clinicalbreakpoints used to interpret the results of sensitivity tests for dog and cat isolates in both agents. Theobserved resistance in this study might be related to the regular use of fluoroquinolones and third generationcephalosporins. Therefore, the use of ‘critically important antimicrobials with highest priorityfor human medicine’ remains an important issue in small animal veterinary medicine.