Ischemic stroke has a high recurrence rate despite treatment. This underlines the significance of investigating new possible cerebrovascular risk factors, such as the acquired gene mutation JAK2V617F found in 3.1% of the general population. We aimed to investigate the prevalence of the JAK2V617F mutation in an ischemic stroke population compared with matched controls. We enrolled 538 consecutive Danish patients with ischemic stroke (mean age 69.5± 10.9, 39.2% female) within seven days of symptom onset. Using multiple adjusted conditional logistic regression analysis, we compared the prevalence of JAK2V617F with age- and sex-matched controls free of ischemic cerebrovascular disease (ICVD) from the Danish General Suburban Population Study. DNA was analyzed for the JAK2V617F mutation using sensitive droplet digital PCR in patients and controls. Of the 538 patients with ischemic stroke, 61 (11.3%) had the JAK2V617F mutation. There were no differences in patient demographics or cerebrovascular comorbidities between patients with and without mutations. Patients with ischemic stroke were more likely to have the JAK2V617F mutation compared with matched controls in whom the JAK2V617F prevalence was 4.4%% (odds ratio (OR)=2.37, 95% CI [1.57, 3.58], p<0.001). A subanalysis stratified by smoking history revealed that the association was strongest in current smokers (OR=4.78, 95% CI [2.22, 10.28], p<0.001). Patients with ischemic stroke are 2.4 times more likely to have the JAK2V617F mutation than matched controls without ICVD when adjusting for other cerebrovascular risk factors. This finding supports the JAK2V617F mutation as a novel cerebrovascular risk factor.