There is a growing concern that air pollution, especially those particles <2.5 μm (PM), could increase the risk of cognitive impairment and mental disorders. However, the relationship between ambient PM and neuropsychiatric symptoms in people with cognitive impairment is still undetermined. This longitudinal study included 645 pairs of cognitively impaired subjects, who had not changed residence within Seoul, and their caregivers from the Clinical Research Center for Dementia of South Korea study cohort between September 2005 and June 2010 (1763 days). Neuropsychiatric symptoms were measured by the Korean version of the Neuropsychiatry Inventory, and caregiver burden was examined by the Neuropsychiatry Inventory Caregiver Distress Scale at the first and second visits at the outpatient clinic. District-specific PM concentrations were constructed over 1 month to 1 year prior to each visit. A log-linear regression using generalized estimating equations to account for repeated measures was used to assess the relationship between PM exposure and neuropsychiatric symptoms or caregiver burden. Aggravated neuropsychiatric symptoms were associated with exposure to high PM levels (adjusted percent change: 16.7% [95% confidence interval (CI), 5.0-29.7] per 8.3 μg/m increase in 1-month moving averages). Increased caregiver burden was associated with high PM exposures only in caregivers for patients with Alzheimer's disease (adjusted percent change: 29.0% [95% CI, 8.1-53.9] per 8.3 μg/m increase in 1-month moving averages). The present results indicate that PM exposure is associated with aggravated neuropsychiatric symptoms and increased caregiver burden in subjects with cognitive impairment. The findings in this study suggest that the role of air pollution deserves great consideration in the aging population with cognitive impairment.