Background There is no robust evidence that screening patients with acute stroke for dysphagia reduces the risk of stroke-associated pneumonia (SAP), or of how quickly it should be done after admission. We aimed to identify if delays in bedside dysphagia screening and comprehensive dysphagia assessments by a speech and language therapist (SALT) were associated with patients' risk of SAP. Methods Nationwide, registry-based, prospective cohort study of patients admitted with acute stroke in England and Wales. Multilevel multivariable logistic regression models were fitted, adjusting for patient variables and stroke severity. The exposures were time from (1) admission to bedside dysphagia screen, and (2) admission to comprehensive dysphagia assessment. Results Of 63 650 patients admitted with acute stroke, 55 838 (88%) had a dysphagia screen, and 24 542 (39%) a comprehensive dysphagia assessment. Patients with the longest delays in dysphagia screening (4th quartile adjusted OR 1.14, 1.03 to 1.24) and SALT dysphagia assessment (4th quartile adjusted OR 2.01, 1.76 to 2.30) had a higher risk of SAP. The risk of SAP increased in a dose-response manner with delays in SALT dysphagia assessment, with an absolute increase of pneumonia incidence of 1% per day of delay. Conclusions Delays in screening for and assessing dysphagia after stroke, are associated with higher risk of SAP. Since SAP is one of the main causes of mortality after acute stroke, early dysphagia assessment may contribute to preventing deaths from acute stroke and could be implemented even in settings without access to high-technology specialist stroke care.