Background: Idiopathic aortitis became recognized relatively recently, and the body of knowledge concerning this condition is scarce. We aimed to determine the frequency of idiopathic aortitis in aortic specimens, the clinical, laboratory and radiologic characteristics at diagnosis and during follow-up, and the approach to investigation, treatment and monitoring taken by the treating physicians. Methods:We identified cases of aortitis diagnosed on pathological specimens of the aorta between Jan. 1, 2003, and July 31, 2013, at The Ottawa Hospital by reviewing the hospital's pathology database. Charts of identified patients were reviewed, and data on patient demographic characteristics, clinical features, laboratory and imaging tests, treatment and outcomes were analyzed.Results: A total of 684 aortic specimens were analyzed during the study period; 47 cases of aortitis were identified, 32 of which were idiopathic. Twenty-one patients (66%) had complete imaging of branch vessels at baseline, 16 (76%) of whom had additional aortic or branch vessel lesions. Twelve patients (38%) received corticosteroids postoperatively. Over a mean follow-up period of 47.5 months, among the 12 patients (38%) who had complete imaging of branch vessels at least once, new aortic or branch lesions were diagnosed in 5 (42%); 3/32 patients (9%) required additional vascular surgery; and a new systemic condition was diagnosed in 2/32 (6%).Interpretation: Idiopathic aortitis is commonly discovered incidentally on examination of the pathological specimen following ascending aortic aneurysm repair. No guidelines exist for the investigation, treatment and follow-up of this condition, resulting in great variability of practice. Good-quality prospective studies are needed to address the many unanswered clinical questions regarding idiopathic aortitis and to allow formulation of more definitive recommendations. Abstract ResearchResearch CMAJ OPEN E484CMAJ OPEN, 5(2)