Improved medical care over more than five decades has markedly increased life expectancy, from 12 years to approximately 60 years, in people with Down syndrome (DS). With increased survival into late adulthood, there is now a greater need for the medical care of people with DS to prevent and treat aging-related disorders. In the wider population, acquired cardiovascular diseases such as stroke and coronary heart disease are common with increasing age, but the risks of these diseases in people with DS are unknown. There are no population-level data on the incidence of acquired major cerebrovascular and coronary diseases in DS, and no data examining how cardiovascular comorbidities or risk factors in DS might impact on cardiovascular event incidence. Such data would be also valuable to inform health care planning for people with DS. Our objective was therefore to conduct a population-level matched cohort study to quantify the risk of incident major cardiovascular events in DS.A population-level matched cohort study compared the risk of incident cardiovascular events between hospitalized patients with and without DS, adjusting for sex, and vascular risk factors. The sample was derived from hospitalization data within the Australian state of Victoria from 1993-2010. For each DS admission, 4 exact age-matched non-DS admissions were randomly selected from all hospitalizations within a week of the relevant DS admission to form the comparison cohort. There were 4,081 people with DS and 16,324 without DS, with a total of 212,539 person-years of observation. Compared to the group without DS, there was a higher prevalence in the DS group of congenital heart disease, cardiac arrhythmia, dementia, pulmonary hypertension, diabetes and sleep apnea, and a lower prevalence of ever-smoking. DS was associated with a greater risk of incident cerebrovascular events (Risk Ratio, RR 2.70, 95% CI 2.08, 3.53) especially among females (RR 3.31, 95% CI 2.21, 4.94) and patients aged ≤ 50 years old. The association of DS with ischemic strokes was substantially attenuated on adjustment for cardioembolic risk (RR 1.93, 95% CI 1.04, 3.20), but unaffected by adjustment for atherosclerotic risk. DS was associated with a 40-70% reduced risk of any coronary event in males (RR 0.58, 95% CI 0.40, 0.84) but not in females (RR 1.14, 95% CI 0.73, 1.77).DS is associated with a high risk of stroke, expressed across all ages. Ischemic stroke risk in DS appears mostly driven by cardioembolic risk. The greater risk of hemorrhagic stroke and lower risk of coronary events (in males) in DS remain unexplained.