Aneurysm formation after abdominal aortic bypass reconstruction is an infrequent but underestimated complication. Aneurysms may occur after aortic prosthetic reconstruction for both occlusive and aneurysmal disease, may occur early or late, and may be classified as a pseudoaneurysm or true aneurysm.Thirty-one cases in 29 patients treated at a tertiary referral center from 1980 to 1992 were retrospectively reviewed. Iliac and femoral aneurysms were excluded. The indication for initial abdominal aortic grafting had been aneurysmal disease in 19 patient and occlusive disease in 10 patients.There were 25 pseudoaneurysms and six true aneurysms, the latter followed grafting for aneurysmal disease. The current aneurysm (mean size 7.1 cm) was at the proximal aortic anastomosis in 27 cases and at the distal aortic anastomosis in two cases. Symptoms at presentation included abdominal pain (14), mass (12), claudication (9), back pain (6), and gastrointestinal bleeding (3). Surgical management included interposition tube grafting (16), aortoiliofemoral bypass (9), and graft removal with extraanatomic bypass (3). The overall operative morbidity rate was 73%, and mortality rate was 21%.Paraanastomotic aortic aneurysms are being increasingly recognized and are associated with high morbidity and mortality rates. Patients should be periodically studied after aortic grafting with abdominal ultrasonography for early detection of this potentially serious complication. Elective surgical repair is advocated in the effort to minimize morbidity rates.