BACKGROUND: Recent studies have identified a high frequency of Clostridium difficile infections in patients with active inflammatory bowel disease. AIMS: To retrospectively assess the determinants and results of Clostridium difficile testing upon the admission of patients hospitalized with active inflammatory bowel disease in a tertiary care centre and to determine the predicting factors of Clostridium difficile infections. METHODS: We reviewed all admissions from January 2008 and December 2010 for inflammatory bowel disease flare-ups. A toxigenic culture and a stool cytotoxicity assay were performed for all patients tested for Clostridium difficile. RESULTS: Out of 813 consecutive stays, Clostridium difficile diagnostic assays have been performed in 59% of inpatients. The independent predictive factors for the testing were IBD (ulcerative colitis: OR 2.0, 95% CI 1.5-2.9; p<0.0001) and colonic involvement at admission (OR 2.2, 95% CI 1.5-3.1, p<0.0001). Clostridium difficile infection was present in 7.0% of the inpatients who underwent testing. In a multivariate analysis, the only independent predictor was the intake of nonsteroidal anti-inflammatory drugs within the two months before admission (OR 3.8, 95% CI 1.2-12.3; p=0.02). CONCLUSIONS: Clostridium difficile infection is frequently associated with active inflammatory bowel disease. Our study suggests that a recent intake of nonsteroidal anti-inflammatory drugs is a risk factor for inflammatory bowel disease -associated Clostridium difficile infection.