The authors evaluate the usefulness of magnetic resonance (MR) imaging in the diagnosis of Takayasu arteritis (TA). MR images of 77 patients with TA (74 women, three men) were obtained with a 1.5-T system, and the resulting images were compared with those obtained at conventional angiography. Aortic lesions--including stenosis, dilatation, aneurysms, wall thickening, and mural thrombi--were clearly visualized at MR imaging, particularly in aortic long-axis images. Further, aortic regurgitation, which occurs frequently in patients with TA, was clearly seen in cine MR images. Also, aortic branch vessel lesions adjacent to the aortic arch were well visualized, although distal lesions were often not as clear. Pulmonary arterial lesions, including occlusion and dilatation, were seen as well. The authors conclude that MR imaging can clearly depict various vascular lesions in both the systemic and pulmonary arteries of patients with TA, thus enabling a definitive diagnosis of the disease.