This study will investigate the safety and effectiveness of the drug Leflunomide to treat uveitis-an inflammation of the eye caused by an immune system abnormality. Leflunomide suppresses immune system activity and has been shown to control autoimmune diseases, such as arthritis (joint inflammation), in animals. It has also improved symptoms in patients with rheumatoid arthritis, and the Food and Drug Administration has approved it for treating patients with this disease. Eye and joint inflammation may have similar causes, and medicines for arthritis often help patients with eye inflammation. This study will examine whether Leflunomide can help patients with uveitis.