Investigators form the National Institutes of Health (NIH), in the United States, have prospectively studied 60 patients with Takayasus's arteritis over a period of 20 years. Unique observations resulted from the requirement that all patients be part of Institutional Review Board-approved standardized protocols that required periodic complete clinical, laboratory and angiographic evaluations, regardless of degree of disease activity. Patients judged to have active disease received protocol defined treatment that always included prednisone, and to which cytotoxic agents were added in the event that relapse followed tapering or withdrawal of corticosteroids. The prospective standard approach applied to this cohort has provided new insights into the presentation, course and treatment-responsiveness of Takayasu's arteritis. This article will focus on the questions raised by this study and implications for patient care.