Ultrasound is a useful imaging modality for the diagnosis of giant cell arteritis. Ultrasound of temporal arteries is recommended as the first imaging modality in patients with suspected predominantly cranial giant cell arteritis. The thickening of the arterial wall (halo sign) is the ultrasound finding most suggestive of giant cell arteritis. In patients in whom there is a high clinical suspicion of giant cell arteritis and a halo sign, the diagnosis of giant cell arteritis may be made without temporal artery biopsy.