OBJECTIVE To describe clinical characteristics and evaluate processes of care and outcomes at discharge in patients with ischemic stroke with and without preexisting dementia. METHODS Retrospective cohort study using the Registry of the Canadian Stroke Network including patients presenting with an acute ischemic stroke between 2003 and 2008. Preexisting dementia was defined as any type of dementia that was present prior to the index stroke case. Palliative patients were excluded. Demographic information, clinical presentation, selected process measures (e.g., thrombolysis, admission to stroke unit, carotid imaging, stroke prevention), pneumonia, death, disability, and disposition at discharge were analyzed. RESULTS Among 9,304 eligible patients with an acute ischemic stroke, 702 (9.1%) had a history of dementia. Patients with dementia were older (mean age 81 vs 70 years; p < 0.001), had more severe strokes (Canadian Neurological Scale score <4, 20.7% vs 10.5%; p < 0.001), and were more likely to have atrial fibrillation (22.8% vs 15.3%; p < 0.001) than those without dementia. Patients with dementia were slightly less likely to be admitted to a stroke unit (63% vs 67.6%; odds ratio [OR] 0.82, 95% confidence interval [CI] 0.70-0.96) or to receive thrombolysis (10.5% vs 15.7%; OR 0.63, 95% CI 0.49-0.81). There were no differences in other performance measures. Patients with preexisting dementia had higher disability at discharge (OR 3.20, 95% CI 2.64-3.87) and were less likely to be discharged to their prestroke place of residence (24% vs 45%; p < 0.001). CONCLUSIONS In patients with stroke, preexisting dementia is associated with high rates of disability and institutionalization, representing an increasing challenge for the health care system.