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Background Clostridium difficile infections (CDI) are the most frequent cause of diarrhoea in hospitals. Geriatric patients are more often affected by the condition, by a relapse and complications. Therefore, a crucial question is how often colonization with toxigenic Clostridium difficile strains occurs in elderly patients without diarrhoea and whether there is a “risk pattern” of colonized patients that can be defined by geriatric assessment. Furthermore, the probability for those asymptomatic carriers to develop a symptomatic infection over time has not been sufficiently explored. Methods We performed a cohort study design to assess the association of clinical variables with Clostridium difficile colonization. The first stool sample of 262 consecutive asymptomatic patients admitted to a geriatric unit was tested for toxigenic Clostridium difficile using PCR (GeneXpert, Cepheid). A comprehensive geriatric assessment (CGA) including Barthel Index, Mini Mental State Examination (MMSE) and hand grip-strength was performed. In addition, Charlson Comorbidity Index, body mass index, number and length of previous hospital stays, previous treatment with antibiotics, institutionalization, primary diagnoses and medication were recorded and evaluated as possible risk factors of colonization by means of binary logistic regression. Secondly, we explored the association of C. difficile colonization with subsequent development of CDI during hospital stay. Results At admission, 43 (16.4%) patients tested positive for toxin B by PCR. Seven (16.3%) of these colonized patients developed clinical CDI during hospital stay, compared to one out of 219 patients with negative or invalid PCR testing (Odds ratio 12,3; Fisher’s exact test: p  = 0.000). Overall, 7 out of 8 (87.5%) CDI patients had been colonized at admission. Risk factors of colonization with C. difficile were a history of CDI, previous antibiotic treatment and hospital stays. The parameters of the CGA were not significantly associated with colonization. Conclusion Colonization with toxigenic Clostridium difficile strains occurs frequently in asymptomatic patients admitted to a geriatric unit. Previous CDI, antibiotic exposure and hospital stay, but not clinical variables such as CGA, are the main factors associated with asymptomatic Clostridium difficile carriage. Colonization is a crucial risk factor for subsequent development of symptomatic CDI.