Early diagnosis and treatment are pivotal for patients with acute aortic dissection (AAD). D-dimer is a rule-out diagnostic test for pulmonary embolism but there is evidence that it may also be applicable to AAD. We evaluated plasma D-dimer, white cell blood count (WBC), C-reactive protein (CRP) and N-terminal pro-B-type natriuretic peptide (BNP) in 18 consecutive patients with established AAD, 21 consecutive patients with dilated ascending aortas scheduled for elective surgery and 8 normal subjects. Patients with AAD had significantly higher elevated D-dimer, compared to chronic aneurysms and normal controls (p<0.0001). D-dimer level higher than 700 ng/ml had a sensitivity of 94% and specificity of 59% for diagnosis of AAD. The WBC count was also significantly increased compared to the other groups (p<0.01). CRP and BNP values were significantly higher compared to normal controls but these parameters did not distinguish between AAD and chronic aneurysms. D-dimer can be used as a 'rule-out' test in patients with suspected AAD and seems useful in the discrimination between AAD and chronic uncomplicated aneurysms, unlike CRP and BNP plasma levels.