Antimicrobial susceptibility testing is often used to guide antibiotic selection for cystic fibrosis (CF) exacerbations; however, there is concern regarding the accuracy of automated systems, particularly for P. aeruginosa. The primary objective of this study was to evaluate the accuracy of the BD Phoenix™ Automated Microbiology System in determining susceptibility of P. aeruginosa. Clinical isolates form CF respiratory specimens were included. Susceptibility testing was performed via broth microdilution (BMD), disk diffusion (DD), and the BD Phoenix™. Minor, major, and very major errors were compared between the three methods. Forty-seven P. aeruginosa isolates were included; categorical agreement was 87.8% for the BD Phoenix™ and 87.9% for DD, compared to BMD. Both methods were found to have higher than acceptable error rates.