Background A rapid laboratory test for diagnosis of acute aortic dissection (AAD) has not been available. We performed this prospective study to determine the utility of a rapid bedside D-dimer (DD) assay for detection of AAD. Methods and Results Patients with suspected AAD were recruited and their DD levels were measured by rapid bedside assay. They were divided into 2 groups according to enhanced computed tomography findings: an AAD group (n=30) and a non-AAD group (n=48). The median DD level was higher in the AAD group (1.80 μg/ml) than in the non-AAD group (0.42 μg/ml) (p=0.000). The rapid bedside DD assay showed 100% sensitivity, 54% specificity, 58% positive predictive value and 100% negative predictive value for detection of AAD with a normal DD level of up to 0.5 μg/ml. The combination of DD level >0.5 μg/ml and systolic blood pressure ≥180 mmHg showed 86% positive predictive value for detection of AAD. Conclusions We conclude that the rapid bedside DD assay is a highly sensitive method for early exclusion of AAD in patients with chest and/or back pain suggestive of AAD. Acute aortic dissection is highly probable if a rapid DD assay shows the elevated DD level with systolic blood pressure ≥180 mmHg on admission. (Circ J 2005; 69: 397 - 403)