IN THE age group in which aneurysms of the abdominal aorta usually occur, malignant neoplasia has a high relative incidence (Fig 1). In slightly over 800 cases of abdominal aortic aneurysms which we observed during the past 22 years, a coincidental malignancy was encountered in 31 instances, or in about 4% of all cases. The coincidence of two potentially lethal lesions raises obvious problems of management, particularly as regards priority of treatment. The goal of the present study is to summarize our experience for the establishment of guidelines that may prove helpful in the management of these problems. Case Material As shown in Table 1, the clinical material surveyed included 803 cases of abdominal aortic aneurysms, of which 570 were surgically treated and 233 were conservatively managed. The 31 malignant lesions associated with the aneurysms came under observation in four principal ways: 1. An abdominal aortic aneurysm was diagnosed after