Giant-cell arteritis (also called temporal arteritis) involves inflammation of large and medium-sized arteries (vasculitis). This condition occurs in elderly people and can lead to sudden blindness when the inflammation involves the temporal artery, an artery located on the side of the head that supplies blood to the eye. Prompt treatment can prevent blindness. Standard therapy for giant-cell arteritis consists of large doses of the drug prednisone, followed by a gradual decrease in the dose. Patients need to take a low dose of prednisone for an average of 2 years. Unfortunately, in many patients, symptoms (including headache, changes in vision, and tenderness over the temporal artery) return as the dose of prednisone is lowered, or side effects from the prednisone develop. Thus, better ways to treat giant-cell arteritis are needed. Methotrexate is a drug that interacts with the immune system and is useful in treating other forms of vasculitis. Some reports suggest that it may help decrease the amount of prednisone needed to treat giant-cell arteritis.