BACKGROUND: Dementia is a serious, chronic, and costly public health problem. Prior studies have described dementia as increasing length of hospital stay, but so far no explanations have been proposed. METHODS: To identify early markers for prolonged hospital stay in demented elderly inpatients, 178 community-dwelling or institutionalized subjects aged 75+, hospitalized through an emergency department in 9 teaching hospitals in France, were analyzed. Prolonged hospital stays were defined according a limit adjusted for Diagnosis Related Group. All patients underwent a comprehensive geriatric assessment at admission. Logistic regression multifactorial mixed model was performed. Center effect was considered as a random effect. RESULTS: Of the 178 stays, 52 were prolonged. Most concerned community-dwelling patients (86%). Multifactor analysis demonstrated that demographic variables had no influence on the length of stay, while diagnosis of delirium (OR 2.31; 95% CI 1.77 - 2.91), walking difficulties (OR 1.94; 95% CI 1.62 - 2.43) and report by the informal caregiver of moderate or severe burden (OR 1.52; 95% CI 1.19 - 1.86) or low social quality-of-life score (OR 1.25; 95% CI 1.03 - 1.40), according to the Zarit's Burden Inventory short scale (12 items) and the Duke's Health Profile respectively, were identified as early markers for prolonged hospital stays. CONCLUSION: At the time of the rising incidence of cognitive disorders, these results suggest that preventive approaches might be possible. In a hospital setting as well as in a community-dwelling population, more specific, specialized and coordinated care, using the expertise of multiple disciplines appears as a probable effective measure to limit prolonged hospital stay. Such approaches require (i) clear patient-oriented goal definition, (ii) understanding and appreciation of roles among various health care and social disciplines and, (iii) cooperation between partners in patient's management. However, the cost- and health-effectiveness of such approaches should be evaluated.