OBJECTIVE Acute myocardial infarction is expected to be an important medical complication following ischaemic stroke. We sought to describe the frequency and clinical impact of in-hospital myocardial infarction following acute ischaemic stroke. METHODS Consecutive patients with acute ischaemic stroke were identified from the Registry of the Canadian Stroke Network (2003-2006). Stroke severity was measured using the Canadian Neurological Scale (CNS). Functional status at discharge was measured with the modified-Rankin Scale, and categorized into strokes with no or mild-moderate dependency (m-Rankin 0-3) and those with severe dependence or death (m-Rankin 4-6). Multivariable logistic regression was used to determine the association between myocardial infarction and clinical outcome (death or severe dependence at hospital discharge and 1 year mortality), independent of co-morbidities and in-hospital medical complications. RESULTS In total, 9180 patients with acute ischaemic stroke were included. The mean age was 72 years (SD 13.9) and 48% were female. Overall, 211 (2.3%) patients were reported to have myocardial infarction during hospitalization. At hospital discharge, 64.9% of patients with in-hospital myocardial infarction had died or were severely disabled, compared with 35.8% in the entire cohort. Mortality at 1 year after ischaemic stroke was 56.4% in patients with myocardial infarction and 21.9% in the entire cohort. On multivariable analyses, myocardial infarction was also associated with death or severe dependence at discharge (OR 2.51; 95%CI 1.75-3.59) and mortality within 1 year (HR 1.83; 95%CI 1.51-2.23). Previous history of myocardial infarction (OR 1.50; 95%CI 1.05-2.15), diabetes mellitus (OR 1.55; 95%CI 1.42-2.10), stroke severity (OR 1.13; 95% CI 1.09-1.17) and peripheral vascular disease (OR 1.61; 95%CI 1.04-2.49) were independently associated with myocardial infarction during hospitalization. CONCLUSIONS Myocardial infarction is an important medical complication after acute ischaemic stroke.