In order to diagnose thrombus and to evaluate blood flow in aortic diseases, we investigated the usefulness of tagging cine magnetic resonance imaging (MRI) in patients with aortic aneurysm and aortic dissection. Six abdominal aortic aneurysms, two aortic arch aneurysms and three aortic dissections were examined with use of tagging cine MRI. Linear tagging bands were 3 or 5 mm width and established to the long and short axial images of the aortic lesions. Tagging bands were confirmed as the low-intensity signal bands in all patients. The parts of tagging bands of the intraaortic thrombus didn't move, whereas the parts of tagging bands of the intraaortic blood flow moved and faded as time passed. Intraaortic thrombi were diagnosed in eight patients (6 abdominal aortic aneurysms, 1 aortic arch aneurysm, and 1 aortic dissection) in accordance with the stain of the parts of tagging bands. In patients with aortic dissection, the parts of tagging bands in the false lumen moved slowly, whereas the parts of tagging bands in the true lumen moved fast. Tagging cine MRI has been shown to be useful in the diagnosis of thrombus and blood flow in aortic diseases.