Clostridium difficile is the most common cause of hospital-associated diarrhoea. Contaminated hospital surfaces are a major source of transmission. Effective eradication of C. difficile spores from the hospital environment is one of the key interventions in controlling transmission. The purpose of this study was to evaluate the effectiveness of a targeted environmental cleaning programme using a bleach-based decontamination regimen in reducing the incidence of healthcare-associated Clostridium difficile colitis in a large multi-hospital healthcare system. The study results indicate that a bleach cleaning intervention programme may significantly reduce the incidence of new onset healthcare-associated Clostridium difficile-associated diarrhoea during the flu season, when antibiotic use in the hospital is highest. 5th International conference on healthcare infections March 2010 poster number 146, Society for healthcare Epidemiology of infections. Friday, March 19, 2010. Grand Hall (Hyatt Regency Atlanta).