Most classical manifestations of giant cell arteritis (GCA) are the result of occlusive vascular involvement. However, unlike ischemic manifestations, aortic aneurysmal disease in patients with GCA has been less well described. We assessed the incidence and predictors of aortic aneurysm and dissection in patients with biopsy-proven GCA from the Lugo region of northwestern Spain and compared the results with those in a 2003 report from Olmsted County, MN. We performed a retrospective study of biopsy-proven GCA patients diagnosed from 1981 to 2001 at the single hospital for a well-defined population of almost 250,000 people. Twenty (9.5%) of the 210 biopsy-proven GCA patients diagnosed during the study period developed aortic aneurysmal disease. Sixteen of the 20 patients had thoracic aneurysms and 6 had abdominal aneurysms. The incidence of aortic aneurysm and/or dissection in Lugo (18.9 per 1000 person years at risk) was similar to that reported in Olmsted County (18.7 per 1000 person years at risk). Hypertension (hazard ratio: 4.73) and polymyalgia rheumatica with a marked acute inflammatory response at the time of diagnosis of GCA (hazard ratio: 3.71) were the best predictors of aortic aneurysmal disease. Our present observations suggest that a severe inflammatory response associated with hypertension at the time of diagnosis of GCA may promote the development of aortic aneurysmal disease. GCA patients having these features should be monitored for the existence of aortic aneurysm and dissection.