Clostridium difficile infection (CDI) is one of the main causes of diarrhoea associated with antimicrobial therapy. Antibiotics with good 'in vitro' activity against C. difficile could protect patients from developing CDI. In this study, the potential of linezolid to protect patients with ventilator-associated pneumonia (VAP) from developing CDI was assessed. Over a 4-year period, a cohort of patients who developed VAP following major heart surgery (MHS) in Gregorio Marañón General Hospital (Madrid, Spain) was retrospectively analysed. Patients were divided into those who developed CDI in the post-operative period and those who did not. Variables associated with the development of CDI were analysed, including the role of antimicrobial therapy. Overall, 1934 patients underwent MHS; 90 patients were excluded due to intra-operative or early post-operative (first 48h) death, leaving a study population of 1844 patients, of which 105 cases had VAP. Complete clinical data were available in 91 cases. CDI occurred in 22 patients (24.2%). When comparing VAP cases with and without CDI, EuroSCORE and overall antibiotics prescribed were not significantly different. Patients with chronic renal failure (CRF) were more prone to develop CDI than those without CRF (32% vs. 13%; P=0.04), and patients without [corrected] CDI received more doses of linezolid than those with [corrected] CDI [12.4±9.7 defined daily doses (DDDs) vs. 6.7±4.0 DDDs; P=0.007]. Multivariate analysis confirmed that receiving more DDDs of linezolid protects from developing CDI (hazard ratio=0.908, 95% confidence interval 0.83-0.99; P=0.04). This work is retrospective and addresses a very particular population, but it is the first to suggest the potential impact of linezolid against CDI.