Twenty-seven patients with mycotic aneurysms of the aorta and its major branches were operated on between 1969 and 1991. There were 24 males and three females ranging in age from 6 to 84 years (mean age for adults 63 years). Sixteen of the 27 (59%) aneurysms were ruptured and in situ repair was undertaken in 20 (74%) patients. The mean follow-up was 5.8 years (range: 8 months to 16 years). Four patients (15%) died during the hospital stay and 23 survived. There were eight late deaths, two of which were a direct result of the aneurysm. The estimated 1- and 5-year survival rates were 62 and 36%, respectively. Extra-anatomic reconstruction is the method of choice for the majority of patients with mycotic aneurysm of the infrarenal abdominal aorta and iliac arteries. In situ repair after an extensive debridement of the aneurysmal wall and all infected tissue combined with antibiotic therapy is a satisfactory method of treating mycotic aneurysms of other locations, and for a highly selected group of patients with infrarenal mycotic aortic aneurysms.