Imaging studies are necessary to determine disease extension and disease activity in the small-vessel vasculitides. Computed tomography (CT) and magnetic resonance imaging (MRI) increase the number of pathologic findings compared with conventional radiography. MRI delineates mucosal inflammation and granulomas in the paranasal sinuses, whereas CT provides information about osseous lesions. CT is superior to MRI for the detection of pulmonary lesions. Radiograph angiography has been the gold standard for medium- and large-vessel vasculitides for decades. Echocardiography and MRI correspond well with conventional angiography to assess cardiac involvement in Kawasaki disease. MRI, CT, and CT angiography are alternative noninvasive techniques to delineate vasculitic lesions in polyarteritis nodosa, Takayasu's arteritis, and large-vessel giant cell arteritis. Duplex ultrasonography has the greatest resolution. It delineates typical artery wall swelling in temporal arteritis and Takayasu's arteritis. Positron emission tomography can assess inflammatory activity of large arteries.