AIM: To investigate risk factors for severe clostridium difficile associated diarrhoea (CDAD) in hospitalised patients. METHODS: We analysed risk factors for severe CDAD (associated with systemic signs of hypovolemia) in 124 hospitalised patients by retrospective chart review. RESULTS: Severe CDAD was present in 27 patients (22%). Statistical analysis showed a significant association with a higher 30-d mortality (33% vs 4%, P < 0.001) and a higher proportion of longer hospital stay exceeding 14 d (74% vs 52%, P = 0.048). Charlson co-morbidity score (OR 1.29 for 1 point increment, P < 0.05) and serum C-reactive protein at diagnosis (OR 1.15 for 10 mg/L increment, P