Cognitive and behavioural impairment among elderly people in institutions providing different levels of care. OBJECTIVE: To compare the prevalence and degree of cognitive and behavioural impairment in elderly patients in institutions providing different levels of care. DESIGN: Prevalence study. SETTING: A nursing home, a home for the aged and psychogeriatric wards in a provincial psychiatric hospital. PATIENTS: Only subjects 65 years of age or older were eligible for inclusion. A random sample was selected comprising 25% of the residents in the nursing home and the home for the aged; of the 119 asked to participate 95 agreed (44 in the nursing home and 51 in the home for the aged). All 50 on the psychogeriatric wards agreed to participate. MAIN OUTCOME MEASURES: The Mini-Mental State Examination (MMSE) and the Kingston Dementia Rating Scale (KDRS). RESULTS: An MMSE score of less than 24 (cognitive impairment) was given to 37 (84%) of the residents in the nursing home, 43 (84%) of those in the home for the aged and 48 (96%) of the patients in the psychiatric hospital; the corresponding numbers for a KDRS score of more than 0 (cognitive impairment) were 41 (93%), 48 (94%) and 50 (100%). The seven patients receiving the highest level of care at the home for the aged (special care) had more behavioural problems than those in the psychiatric hospital did (p less than 0.001). CONCLUSIONS: Cognitive and behavioural impairment was widespread in the three institutions regardless of the level of care. When planning services and allocating resources government funding agencies should consider the degree and prevalence of such impairment among elderly people in institutions. 