Background Although neuropsychiatric symptoms in dementia are common, there have been few large long-term prospective studies assessing the course of a broad range of neuropsychiatric symptoms in dementia. Objectives To investigate the course of neuropsychiatric symptoms in patients with dementia, including data about prevalence, incidence and persistence. Methods One hundred and ninety-nine patients with dementia were assessed every six months for two-years, using the Neuropsychiatric Inventory (NPI) to evaluate neuropsychiatric symptoms. Results Nearly all patients (95%) developed one or more neuropsychiatric symptoms in the two-year study period. Mood disorders were the most common problem. The severity of depression decreased, whereas the severity of apathy and aberrant motor behaviour increased during follow-up. The cumulative incidence was highest for hyperactive behaviours and apathy. Overall behavioral problems were relatively persistent, but most symptoms were intermittent, with apathy and aberrant motor behaviour being persistent for longer consecutive periods. Conclusions Neuropsychiatric symptoms in dementia are a common and major problem. Different symptoms have their own specific course, most of the time show a intermittent course, but behavioural problems overall are chronically present. The data have implications for developing treatment strategies.