Giant cell arteritis and Takayasu arteritis are separate but similar idiopathic diseases clinically characterized by constitutional symptoms, shared surrogate markers of systemic inflammation and indistinguishable granulomatous pan-arteritis of large vessels. This review emphasizes and analyses changing perceptions about the diseases. Recent series suggest that aortic involvement in giant cell arteritis may be more common than was previously appreciated. The case for and against inflammatory arthritis in giant cell arteritis is discussed. Ethnic new geographical variation in Takayasu arteritis-disease expression is reviewed. New philosophies of treatment are presented for both diseases. Prognosis in giant cell arteritis and its relationship to treatment is analysed. The utility of the laboratory for diagnosis and monitoring disease activity is appraised for each.