Background <p>Stroke-associated pneumonia (SAP) is a common infectious complication of acute ischemic stroke (AIS). Although numerous predictive models for SAP have been proposed, a more objective and easily applicable marker is required. This study evaluated the association between the red cell index (RCI) and SAP in patients with AIS.</p> Methods <p>We analyzed 500 consecutive patients with AIS. SAP was defined based on modified Centers for Disease Control and Prevention criteria. The RCI was calculated using blood sample results according to the following formula: RCI = (red blood cell count [⋅10¹²/L] ⋅ hemoglobin [g/L]) / (lymphocyte count [⋅10⁹/ L] ⋅ platelet count [⋅10⁹/ L])</p> Results <p>Among all patients, 62 (12.4%) developed SAP. In multivariable logistic regression analysis, RCI (adjusted odds ratio = 1.46; 95% confidence interval, 1.08–1.97) remained a significant predictor even after adjusting for confounders. Age, dysphagia, impaired consciousness, white blood cell count, and high-sensitivity C-reactive protein levels were also associated with SAP, independent of RCI. Patients with SAP exhibited worse outcomes during hospitalization and at discharge. Among patients with SAP, those with higher RCI values were more frequently admitted to the intensive care unit (<i>P</i> = 0.037) and required intubation (<i>P</i> = 0.009).</p> Conclusion <p>We demonstrated that a higher RCI was associated with SAP in patients with AIS. Furthermore, elevated RCI was associated with worse outcomes in patients who developed SAP.</p>