Prevention of catheter-related bloodstream infection is a basic objective to optimize patient safety in the ICU. Building on the early success of a patient safety unit-based comprehensive intervention (the Keystone ICU project in Michigan), the Bacteremia Zero project aimed to assess its effectiveness after contextual adaptation at large-scale implementation in Spanish ICUs. Prospective time series. A total of 192 ICUs throughout Spain. All patients admitted to the participating ICUs during the study period (baseline April 1 to June 30, 2008; intervention period from January 1, 2009, to June 30, 2010). Engagement, education, execution, and evaluation were key program features. Main components of the intervention included a bundle of evidence-based clinical practices during insertion and maintenance of catheters and a unit-based safety program (including patient safety training and identification and analysis of errors through patient safety rounds) to improve the safety culture. The number of catheter-related bloodstream infections was expressed as median and interquartile range. Poisson distribution was used to calculate incidence rates and risk estimates. The participating ICUs accounted for 68% of all ICUs in Spain. Catheter-related bloodstream infection was reduced after 16-18 months of participation (median 3.07 vs 1.12 episodes per 1,000 catheter-days, p<0.001). The adjusted incidence rate of bacteremia showed a 50% risk reduction (95% CI, 0.39-0.63) at the end of the follow-up period compared with baseline. The reduction was independent of hospital size and type. Results of the Bacteremia Zero project confirmed that the intervention significantly reduced catheter-related bloodstream infection after large-scale implementation in Spanish ICUs. This study suggests that the intervention can also be effective in different socioeconomic contexts even with decentralized health systems.