Objective: To estimate the 18-month persistence of neuropsychiatric symptoms in dementia in a population-based sample, and to compare the severity of neuropsychiatric symptoms at baseline to the severity at 18-month follow-up. Methods: A population-based sample of 329 residents of Cache County, Utah, diagnosed with dementia was rated on the Neuropsychiatric Inventory (NPI). Of the 204 participants with neuropsychiatric symptoms at baseline (defined as total NPI score >0), NPI data were obtained approximately 18 months later on 117 who were alive and available for follow-up. Results: Eighty-one percent of those with neuropsychiatric symptoms at baseline (defined as total NPI score>0) continued to have at least one symptom at follow-up. Sixty-seven percent of participants with a clinically significant total NPI score (defined as ;4) at baseline continued to have a clinically significant total NPI score at follow-up. Among the ten neuropsychiatric domains assessed at baseline, delusions persisted in 65.5% of individuals, followed by depression (58.3%), and aberrant motor behavior (55.6%), while hallucinations and disinhibition persisted in only 25.0% and 11.1% respectively. In participants who were symptomatic at both baseline and follow-up, the mean severity scores at the two observation points were comparable in all ten neuropsychiatric domains. Conclusions: Neuropsychiatric symptoms in dementia overall were highly persistent. Among those in whom symptoms did persist, symptom severity a year and a half later appeared to be comparable.