In a geographically defined population, we assessed incidence and determinants of aphasia attributable to first-ever ischemic stroke (FEIS). A 1-year prospective, population-based study among the permanent residents of the canton Basle City, Switzerland, was performed using multiple overlapping sources of information. Among 188,015 inhabitants, 269 patients had FEIS, of whom 80 (30%; 95% CI, 24 to 36) had aphasia. The overall incidence rate of aphasia attributable to FEIS amounted to 43 per 100,000 inhabitants (95% CI, 33 to 52). Aphasic stroke patients were older than nonaphasic patients. The risk of aphasia attributable to FEIS increased by 4% (95% CI, 1% to 7%), and after controlling for atrial fibrillation, by 3% (95% CI, 1% to 7%) with each year of patients' age. Gender had no effect on incidence, severity, or fluency of aphasia. Cardioembolism was more frequent in aphasic stroke patients than in nonaphasic ones (odds ratio [OR], 1.85; 95% CI, 1.07 to 3.20). Aphasic patients sought medical help earlier than nonaphasic stroke patients. Still, after controlling for stroke onset-assessment interval, aphasic stroke patients were more likely to receive thrombolysis than nonaphasics (OR, 3.5; 95% CI, 1.12 to 10.96). Annually, 43 of 100,000 inhabitants had aphasia resulting from first ischemic stroke. Advancing age and cardioembolism were associated with an increased risk for aphasia. Severity and fluency of aphasia were not affected by demographic variables.