Summary: One hundred and eighty-eight patients in whom the diagnosis of aneurysm of the abdominal aorta (AAA) was established after 1 January 1960 were followed until their deaths or to 31 December 1979. By the actuarial method, the cumulative 5-year risk of an intact aneurysm progressing to rupture was 35%; the observed 5-year survival rate for patients who had medical management for intact AAA was 33%, for patients who had elective surgery for AAA 74%, for patients who had emergency surgery for ruptured AAA 35%, and for those who did not have surgery for ruptured AAA 0%.Comparison of the non-operated and electively-operated groups of patients showed that the former was disproportionately weighted with older higher-risk patients, suggesting that the difference in survival rates for the two groups might be a reflection of patient selection rather than of surgical intervention. Comparison of the cumulative 5-year risk of rupture of an intact AAA with the cumulative 5-.year mortality rate associated with elective surgery for intact AAA showed that elective surgery for intact AAA might be expected to result in a reduction in the cumulative 5-year mortality rates of patients with intact AAA.