Few studies have explored the role of air pollution in neurodegenerative processes, especially various types of dementia. Our aim was to evaluate the association between long-term exposure to air pollution and first hospitalization for dementia subtypes in a large administrative cohort. We selected 350,844 subjects (free of dementia) aged 65-100 years at inclusion (21/10/2001) and followed them until 31/12/2013. We selected all subjects hospitalized for the first time with primary or secondary diagnoses of various forms of dementia. We estimated the exposure at residence using land use regression models for nitrogen oxides (NOx, NO ) and particulate matter (PM) and a chemical transport model for ozone (O ). We used Cox models to estimate the association between exposure and first hospitalization for dementia and its subtypes: vascular dementia (Vd), Alzheimer's disease (Ad) and senile dementia (Sd). We selected 21,548 first hospitalizations for dementia (7497 for Vd, 7669 for Ad and 7833 for Sd). Overall, we observed a negative association between exposure to NO (10 μg/m ) and dementia hospitalizations (HR = 0.97; 95% CI: 0.96-0.99) and a positive association between exposure to O , NOx and dementia hospitalizations, (O : HR = 1.06; 95% CI: 1.04-1.09 per 10 μg/m ; NOx: HR = 1.01; 95% CI: 1.00-1.02 per 20 μg/m ).H. Exposure to NOx, NO , PM , and PM was positively associated with Vd and negatively associated with Ad. Hospitalization for Sd was positively associated with exposure to O (HR = 1.20; 95% CI: 1.15-1.24 per 10 μg/m ). Our results showed a positive association between exposure to NOx and O and hospitalization for dementia and a negative association between NO exposure and hospitalization for dementia. In the analysis by subtype, exposure to each pollutants (except O ) demonstrated a positive association with vascular dementia, while O exposure was associated with senile dementia. The results regarding vascular dementia are a clear indication that the brain effects of air pollution are linked with vascular damage.