BACKGROUND AND PURPOSE: A number of environmental risk factors of acute ischemic stroke have been identified, but few studies have evaluated the influence of the outdoor environment on stroke severity. We assessed the association of residential ambient fine particulate matter air pollution (PM2.5), noise, and surrounding greenspace with initial stroke severity. METHODS: We obtained data on patients hospitalized with acute ischemic stroke from a hospital-based prospective stroke register (2005-2014) in Barcelona. We estimated residential PM2.5 based on an established land use regression model, greenspace as the average satellite-based Normalized Difference Vegetation Index (NDVI) within a 300 m buffer of the residence, and daily (Lday), evening (Levening), night (Lnight) and average noise (Lden) level at the street nearest to the residential address using municipal noise models. Stroke severity was assessed at the time of hospital presentation using the National Institute of Health Stroke Scale (NIHSS).We used logistic regression and binomial models to evaluate the associations of PM2.5, greenspace, and noise with initial stroke severity adjusting for potential confounders. RESULTS: Among 2761 patients, higher residential surrounding greenspace was associated with lower risk of severe stroke (OR for NIHSS>5, 0.75; 95% CI: 0.60-0.95), while, living in areas with higher Lden was associated with a higher risk of severe stroke (OR, 1.30; 95% CI: 1.02-1.65). PM2.5 was not associated with initial stroke severity. CONCLUSIONS: In an urban setting, surrounding greenspace and traffic noise at home are associated with initial stroke severity, suggesting an important influence of the built environment on the global burden of ischemic stroke.