Abstract Body: Background: Cervical artery dissection (CeAD) accounts for a quarter of strokes in young adults. Clinical presentation is often non-specific, leading to a significant proportion of cases being misdiagnosed. This study aims to identify factors contributing to potential misdiagnosis and to assess the impact of misdiagnosis on patient outcomes. Methods:This is a secondary analysis of the Antithrombotics for Stroke Prevention in Cervical Artery Dissection (STOP-CAD), a multicenter cross-sectional international retrospective study of adult patients presenting to an acute care hospital and diagnosed with CeAD. Misdiagnosis of CeAD was determined by identifying any medical encounters for symptoms attributable to the CeAD within the 30 days preceding the diagnosis. Strokes occurring during the interval between the initial misdiagnosis encounter and the final diagnosis date were recorded. We used multivariable regression to identify factors associated with misdiagnosis. The primary outcome was ischemic stroke after CeAD diagnosis. Secondary outcomes included death and excellent functional outcome at 90 days, defined as a modified Rankin Scale (mRS) score <2. Multivariable logistic regression analysis was used to assess the association between misdiagnosis and above outcomes. Results:Of the 4023 patients included in the STOP-CAD study, 4012 were included in this analysis; mean age was 47.5 (+/-13.3) years and 44.6% (1788) were woman. Among these, 663 patients (16.5%) had medical encounters within the 30 days preceding the diagnosis (misdiagnosis group) and 224 (33.8%) had an ischemic stroke after the initial medical encounter but before the CeAD diagnosis. Misdiagnosed patients were younger (OR 0.89, 95% CI 0.83-0.95, p<0.001), more likely to have a history of migraine (OR 1.35, 95% CI 1.09-1.67, p=0.007), present with headache (OR 1.43, 95% CI 1.19-1.71, p<0.001) and less likely to present with signs and symptoms concerning for cerebral ischemia (OR 0.68, 95% CI 0.56-0.83, p<0.001). There was no significant difference in outcomes between the two groups in adjusted analyses: ischemic stroke (aOR 0.96, 95%CI 0.63-1.48, p=0.87), mRS<2 (aOR 1.04, 95% CI 0.76-1.44, p=0.80) and death (aOR 0.58, 95% CI 0.19-1.8, p=0.34). Conclusion: One in six patients who were ultimately diagnosed with CeAD experienced a possible misdiagnosis. Factors associated with a higher likelihood of misdiagnosis included younger age, a history of migraine, and a non-ischemic clinical presentation.