Objective: To improve epidemiological knowledge of neurological deterioration (ND) in patients with acute ischemic stroke (AIS). Methods: In this prospective observational study, we captured ND prospectively in 29,446 AIS patients admitted to 15 hospitals in Korea within 7 days of stroke onset. ND was defined as an increase in National Institutes of Health Stroke Scale (NIHSS) score ≥2 (total), or ≥1 (motor or consciousness), or any new neurological symptoms. Change of incidence rate after stroke...