BACKGROUND d ‐Dimer level is a marker of hypercoagulability, which is associated with thrombus formation and resolution. We investigated the value of d ‐dimer levels in predicting outcomes of acute ischemic stroke in patients who underwent endovascular treatment (EVT). METHODS We analyzed data of patients who underwent only EVT from the SECRET (Selection Criteria in Endovascular Thrombectomy and Thrombolytic Therapy) registry. d ‐Dimer levels were routinely measured in 10 of 15 participating hospitals. Patients were grouped into tertiles (tertile 1, tertile 2, and tertile 3) according to d ‐dimer levels (lowest, moderate, and highest, respectively). We compared serial scores on the National Institutes of Health Stroke Scale at baseline, on day 1 of hospitalization, and at discharge; functional outcome 3 months after EVT; and rate of mortality within 6 months after EVT. RESULTS In the 170 patients, the median d ‐dimer level was 477 ng/mL (interquartile range, 249–988 ng/mL). In tertile 3, the National Institutes of Health Stroke Scale score was higher at discharge than on day 1 of hospitalization. Poor outcome 3 months after EVT (modified Rankin Scale score, ≥3) was more common with high d ‐dimer levels (26.3% of tertile 1, 57.1% of tertile 2, and 76.4% of tertile 3; P <0.001). Multivariable analysis showed that a high d ‐dimer level was independently associated with poor outcome 3 months after EVT (odds ratio [OR], 4.399 [95% CI, 1.594–12.135]). Kaplan–Meier survival analysis showed that a high d ‐dimer level was independently associated with death within 6 months after EVT (OR, 5.441 [95% CI, 1.560–18.978]; log‐rank test, P <0.001). The d ‐dimer effect showed no heterogeneity across the subgroups for poor outcome 3 months after EVT or death within 6 months after EVT. The direction of effect was unfavorable for tertile 3 across all demographic strata. CONCLUSIONS High plasma d ‐dimer levels were predictive of early neurologic worsening, poor functional outcome 3 months after EVT, and death within 6 months after EVT. REGISTRATION URL: http://www.clinicaltrials.gov ; Unique identifier: NCT02964052.