Anastomotic false aneurysm (AFA) of the aorta is a potentially lethal complication after prosthetic grafting. Nineteen aneurysms were encountered in 18 patients within a 30-year period (1960-1991). There were 10 men and 8 women, aged 27-80 years (mean 58 years). In 14 patients, the prostheses were made of silk, in 2 were PTFE, and in 1 each Dacron or silk-Dacron cross-weaved. Patients with an intact AFA had a pulsatile abdominal mass, abdominal pain, an occluded graft and peripheral emboli. Five patients were asymptomatic. Clinical onset of AFA varied from 2 weeks to 12 years (mean 5 years). The accurate rate of diagnosis of single plane angiography was 75% (3 of 4), and computed tomography 100% (ten of ten). Ultrasound was used only once and suggested an AFA. Four AFAs were less than 5cm in diameter. Five patients refused operation and died in 2 years from rupture. Operative mortality was 11% (1 of 9). Treatment was resection of AFA and replacement with a new graft. Life-long follow-up is required for patients with an aortic aneurysm. All ratroperitoneal AFAs should be resected, since the outcome of rupture is poor.