Abstract--Few prospective studies have examined associations between major cardiovascular risk factors and occurrence of abdominal aortic aneurysm; findings from cross-sectional studies are inconsistent. This long-term population-based study assessed relationships of major risk factors in middle-age to clinical nonfatal plus fatal abdominal aortic aneurysm in older-age in the Chicago Heart Association Detection Project in Industry cohort--10 574 men and 8700 women baseline ages 40 to 64 years screened for risk factors in 1967-1973 at workplaces. With average follow-up of 30 years and clinical cases identified from Medicare records and death certificates, risk factor relationships to abdominal aortic aneurysm occurrence were assessed by Cox regression. There were among men 309 cases and among women, 109--most from Medicare records. Most findings were qualitatively similar for men and women. In multivariate analyses (5 models), hazard ratios for abdominal aortic aneurysm were significantly greater for men than women (1.97), with older age (1.63/5 years), higher serum cholesterol (1.30/40.0 mg/dL), cigarettes/d (2.43/20 cigarettes), past smoking (1.41), height (1.17/7 cm), evidence of adverse blood pressure (hazard ratio 1.10/20 mm Hg higher systolic pressure, 1.12 to 1.14/12 mm Hg higher diastolic pressure, 1.87 with history of treated hypertension). It is concluded that major cardiovascular risk factors--serum cholesterol, smoking, and blood pressure--in middle age relate significantly to risk of abdominal aortic aneurysm in persons surviving into older age.