Background: Environmental risk factors for neurodegenerative diseases, an increasing global problem, are largely unknown. Growing evidence suggests that air pollution may contribute to these conditions. We examined the association between exposure to fine particulate matter (PM2.5) and disease progression using Alzheimer's disease (AD), Parkinson's (PD) and amyotrophic lateral sclerosis (ALS) hospitalization data. Methods: We used data on hospital admissions and emergency department visits within New York State (NYS). Our analysis included annual AD, PD, and ALS counts of first hospitalizations (total and sex- and age-stratified) per county from 2000-2014 across NYS. We obtained estimates of annual PM2.5 concentrations at a 1km2 grid resolution from a well-validated prediction model and aggregated estimates to county level. The association was estimated using outcome-specific mixed quasi-Poisson models allowing for outcome-exposure nonlinear relationships. We included county-specific random intercepts and county population size as an offset term, and adjusted for potential confounders.Results: Increase in annual PM2.5 concentration was associated with annual increase in total PD hospitalizations with a steeped slope at lower concentrations (p<0.05). We observed effect modification by age in ALS and PD but not by sex for any of the outcomes. Increase in PM2.5 was nonlinearly associated with increase AD and PD hospitalizations in patients 50-70 years old (p<0.05). We found a linear negative association between PM2.5 exposure and ALS hospitalizations in patients ≥70 (RR=0.94, 95% CI: 0.89-0.99) and a positive among those <70 (RR=1.06, 95% CI: 1.01-1.11). We also found a nonlinear positive association between PM2.5 and PD hospitalizations in females (p<0.001).Discussion: Our findings suggest that annual increase in PM2.5 concentrations, at the county level, may contribute to increases in neurodegenerative disease hospitalization rates in certain patient subpopulations. Further research is needed to better understand PM2.5 differential effects by age and sex in association with these diseases.