Aims There is little knowledge about the predictors of left atrial. appendage (LAA) thrombi in non-vaivular atrial fibrillation (NVAF). We investigated the ability Of D-dimer to predict LAA thrombi. Methods and results In this study, 925 patients with NVAF were enrolled. At the time of transoesophageal echocardiography (TEE), D-dimer levels were measured simultaneously. Significant independent predictors of LAA thrombi were the presence of congestive heart failure [odds ratio (OR) 3.10, 95% confidence interval (Cl) 1.77-5.50, P < 0.0001), a history of recent embolic events (OR 3.39, 95% Cl 1.90-6.04, P < 0.0001), and D-dimer levels (OR 97.6, 95% Cl 17.3-595.8, P < 0.0001). Receiver operating characteristic analysis yielded an optimal cutoff value of 1.15 mu g/mL for D-dimer to detect LAA thrombi. LAA thrombi were detected in 21.8% of patients with higher D-dimer values, whereas it was detected in only 3. 1% of patients with lower D-dimer values. D-dimer cutoff level of 1. 15 mu g/mL had a negative predictive value of 97% for identifying LAA thrombi. Conclusion In patients with NVAF, D-dimer may be helpful for predicting the absence of LAA thrombi. D-dimer level was clinically useful to guide the management of patients with NVAF, especially for those complicated with congestive heart failure and/or recent embolic events.