Noninfectious aortitis may occur in the context of a recognized systemic disease or as a topographically limited lesion without systemic features, which is called clinically isolated aortitis (CIA). This study was undertaken to better define and stress the limitations of this diagnostic category in a large population of patients in a single center dedicated to aortic diseases and to suggest recommendations for care.Records of patients undergoing thoracic aortic surgery (1996-2012) at the Cleveland Clinic were reviewed to identify 196 patients with histopathologically proven aortitis. Clinical diagnoses (giant cell arteritis [GCA], Takayasu arteritis [TAK], CIA, or Other) were determined at the time of surgery. Clinical features, laboratory findings, and imaging results were recorded throughout the follow-up period. At least 6 months of follow-up data were available for 73 CIA patients.The mean age of the patients at time of surgery was 65.6 years (range 15-88 years); 67% of patients were female, and 90.3% were white. At the time of surgery, 129 patients (65.8%) met criteria for CIA, 42 (21.4%) for GCA, 14 (7.1%) for TAK, and 11 (5.6%) met criteria for other systemic inflammatory diseases. During a mean follow-up period of 56.2 months, 19% of CIA patients developed new symptoms, 45% developed new radiographic vascular lesions, 40% underwent additional vascular surgery, and 12% died (n = 9). Eleven of 73 patients (15%) initially classified as having CIA developed features of a systemic disease, most often GCA.The majority of patients (66%) with histopathologically proven aortitis have CIA at the time of surgery. CIA patients infrequently report new symptoms over time, but new vascular lesions requiring surgery commonly occur. Serial follow-up including large vessel imaging is strongly advised for all aortitis patients.