Introduction: Infections caused by multiresistant Pseudomonas aeruginosa (MR-PA) have been associated with persistent infections and high mortality in acquired immunodeficiency syndrome (AIDS) patients. Therefore, understanding the predisposing factors for infection/ colonization by this agent is critical for controlling outbreaks caused by MR-PA in settings with AIDS patients. Objective and methods: To analyze the presence of factors associated with the acquisition of an epidemic MR-PA strain in a hospital with AIDS-predominant admission. A casecontrol study was carried out in which cases and controls were gathered from a prospective cohort of all hospitalized patients in an infectious disease hospital during a five-year study period. Results: Multivariate logistic regression analysis demonstrated that enteral nutrition (OR = 14.9), parenteral nutrition (OR = 10.7), and use of ciprofloxacin (OR = 8.9) were associated with a significant and independent risk for MR-PA acquisition. Conclusions: Although cross-colonization was likely responsible for the outbreaks, the use of ciprofloxacin was also an important factor associated with the acquisition of an epidemic MR-PA strain. More studies are necessary to determine whether different types of nutrition could lead to modification of gastrointestinal flora, thereby increasing the risk for infection/colonization by MR-PA in this population.