Objective: We investigated the relationship between D-dimer levels and long-term major adverse cardiovascular events (MACEs) in masked hypertension patients admitted to the cardiology outpatient clinic. Methods: A total of 512 masked hypertension patients with a median 6 years of follow-up data who underwent serum D-dimer measurement in the hypertension outpatient clinic between April 2014 and June 2016 were retrospectively enrolled. The patients were stratified according to their D-dimer levels and were then divided into tertiles. Clinical outcomes were assessed for MACEs, which were defined as all-cause mortality, cardiovascular mortality, nonfatal myocardial infarction, and nonfatal stroke. Results: The long-term incidence of MACE in masked hypertension patients was higher in the highest tertile of D-dimer. In multivariable analysis, D-dimer was an independent predictor of long-term MACE in masked hypertensive patients (OR: 1.006 [1.004-1.007]; p < 0.001). Compared to the lowest tertile, MACE was approximately 3 times higher in tertile 2 and approximately 10.5 times higher in the highest tertile. In addition, MACE was approximately 3.5 times more common in tertile 3 than in tertile 2. D-dimer was able to predict MACE in patients with masked hypertension (AUC for MACE 0.778; 95% CI: 0.724-0.832; p < 0.001) based on receiver operating characteristic curve analysis. In the Kaplan-Meier curve showing follow-up without MACE (MACE free) according to the D-dimer cutoff value, the long-term incidence of MACE was significantly higher in the high D-dimer group (p < 0.001). Conclusions: D-dimer levels in patients with masked hypertension showed a significant association with increased long-term risk of MACE in this study. (c) 2025 The Author(s)