Objective. @nbsp; To assess the impact of isolation precautions on the incidence of patients colonized or infected with Acinetobacter baumannii (case patients) in a university hospital during the period from 1999 to 2006. Design. @nbsp; Ecological study. Setting. @nbsp; The Besan? University Hospital in France, a 1,200-bed acute care hospital with approximately 50,000 admissions per year. Methods. @nbsp; Using Poisson regression analysis, we evaluated a total of 350,000 patient-days to determine the annual incidence of case patients. This annual incidence was used as the outcome variable, and infection control practices, antibiotic use, and other aggregated data regarding patients' age, sex, McCabe score, and immune status were used as covariates. Results. @nbsp; The implementation of isolation precautions was independently and negatively associated with the incidence of patients colonized or infected with A. baumannii (relative risk, 0.50 [95% confidence interval, 0.40-0.64]; [Formula: see text]). Conclusions. @nbsp; Our study suggests that the implementation of isolation precautions, in addition to standard precautions, effectively prevents the spread of A. baumannii in a hospital setting.