ObjectiveHigh levels ofd-dimer, a marker of thrombotic events, are associated with poor outcomes in patients with various cardiovascular diseases. However, there has been no research on its prognostic implications in acute severe hypertension. This study investigated the association betweend-dimer levels and long-term mortality in patients with severe acute hypertension who visited the emergency department.Design and methodThis observational study included patients with acute severe hypertension who visited the emergency department between 2016 and 2019. Acute severe hypertension was defined as a systolic blood pressure ≥ 180 mmHg or a diastolic blood pressure ≥ 100 mmHg. Among the 10,219 patients, 4,127 who underwentd-dimer assay were analyzed. The patients were categorized into tertiles based on theird-dimer levels at the time of emergency department admission.ResultsAmong the 4,127 patients with acute severe hypertension, 3.1% in the first (lowest) tertile, 17.0% in the second tertile, and 43.2% in the third (highest) tertile died within 3 years. After the adjustment for confounding variables, the third tertile of thed-dimer group (hazard ratio, 6.440; 95% confidence interval, 4.628–8.961) and the second tertile of thed-dimer group (hazard ratio, 2.847; 95% confidence interval, 2.037–3.978) had a significantly higher risk of all-cause mortality over 3 years than the first tertile of thed-dimer group.Conclusionsd-dimer may be a useful marker for identifying the risk of mortality among patients with acute severe hypertension who visit the emergency department.Supplementary InformationThe online version contains supplementary material available at 10.1186/s40885-023-00244-7.