Behavioural problems in dementia are a burden for patients and caregivers and are often the main reason for admission to a nursing home. Research on the prevalence of behavioural problems is scarce. In this study the prevalence of behavioural problems was estimated in nursing home patients with dementia. In 59 demented patients the Neuropsychiatric Inventory (NPI-NH) and the Cohen-Mansfield Agitation Inventory were used to measure behavioural problems over the last two weeks. Behavioural problems were present in about 85% of the study group. Using the NPI-NH aggression/agitation and apathy were present in almost 40% of the patients. Delusions, hallucinations, depression and anxiety were present in 10-15% of the patients. Using the CMAI cursing/verbal aggression, restlessness, complaining, negativism, and mannerisms were prevalent in 30%-50% of the patients. Larger studies on the prevalence of problem behaviour and possibly influencing factors are necessary.