A retrospective study of the susceptibility to antimicrobials (amikacin, tobramycin, gentamicin, ceftazidime, cefepime, piperacillin, piperacil-lin-tazobactam, imipenem, meropenem and ciprofloxacin) of 5,811 Pseudomonas aeruginosa isolates was performed in a general hospital over a period of 12 years. The majority of isolates was from respiratory samples (31.99%), followed by urine samples (26.36%) and ear samples (10.51%). There was a predominance of hospital strains (69.66%); 50.30% of those from medical services, 31.74% from critical care services (mainly ICU) and the remaining from surgical services. No antimicrobial included in our study showed an activity over all isolated strains. In health centers the majority of antimicrobials showed good activity, with a percentage of resistance less than 10%. However, hospital strains showed that only amikacin, piperacillin-tazobactam and meropenem had a percentage of resistance near or lower than 10%. In both environments, gentamicin presented with the highest percentage of resistance. Strains from patients hospitalized in critical care services showed an elevated resistance to tobramycin, imipenem and ceftazidime, while strains from patients in medical services showed resistance to ciprofloxacin. Similar studies published in Spain confirm the importance of conducting local studies in order to understand the antimicrobial susceptibility of P. aeruginosa in each region, and especially to carry out empirically based treatments.