Background Cervical artery dissection (CeAD) is a common cause of stroke in young adults but is frequently misdiagnosed due to its nonspecific symptoms. This study examines factors associated with possible diagnostic error in CeAD and evaluates its impact on patient outcomes. Methods We conducted a secondary analysis of the STOP‐CAD (Antithrombotic Therapy for Stroke Prevention in Cervical Artery Dissection) study, which is a multicenter international study of adult patients admitted with CeAD. Possible diagnostic error was defined as the presence of CeAD symptoms within 30 days before the index CeAD diagnosis. The comparison group included patients diagnosed on their first medical encounter. Multivariable regression was used to identify factors associated with possible diagnostic error. Primary and secondary outcomes included ischemic stroke, death, and modified Rankin Scale score <2. Results Of 4012 patients (mean age 47.5 years, 44.6% female), 663 (16.5%) experienced possible diagnostic error. Among these, 224 (33.8%) reported to have ischemic stroke before CeAD diagnosis. Patients with possible diagnostic error were younger (odds ratio [OR], 0.89, P <0.001), more likely to have a history of migraines (OR, 1.35, P =0.007), and more likely to present with headaches (OR, 1.43, P <0.001), but less likely to show focal neurologic signs (OR, 0.68, P <0.001). There was no significant difference between groups in ischemic stroke after diagnosis (adjusted OR, 0.96, P =0.86), 90‐day modified Rankin Scale score <2 (adjusted OR, 1.04, P =0.80), or death (adjusted OR, 0.58, P =0.34). Conclusions One in 6 patients with CeAD experienced a possible diagnostic error, particularly those who were younger, had migraines, or presented with headaches and nonfocal symptoms.