OBJECTIVE: To determine factors associated with colonization by carbapenem-resistant Pseudomonas aeruginosa and multiresistant Acinetobacter spp. METHODS: Surveillance cultures were collected from patients admitted to the intensive care unit at admission, on the third day after admission and weekly until discharge. The outcome was colonization by these pathogens. Two interventions were implemented: education and the introduction of alcohol rubs. Compliance with hand hygiene, colonization pressure, colonization at admission and risk factors for colonization were evaluated. RESULTS: The probability of becoming colonized increased during the study. The incidence density of colonization by carbapenem-resistant P. aeruginosa and multiresistant Acinetobacter spp. and colonization pressure were different between periods, increasing gradually throughout the study. The increase in colonization pressure was due to patients already colonized at admission. The APACHE II score, colonization pressure in the week before the outcome and male gender were independent risk factors for colonization. Every 1% increase in colonization pressure led to a 2% increase in the risk of being colonized. CONCLUSION: Colonization pressure is a risk factor for carbapenem-resistant P. aeruginosa and multiresistant Acinetobacter spp. colonization. When this pressure reaches critical levels, efforts primarily aimed at hand hygiene may not be sufficient to prevent transmission.