We assessed whether the causes of aortic aneurysm underlying its distinctive geographical distribution in England and Wales act early or later in life from the OPCS data on deaths in England and Wales during April 1969-December 1972. From these data, we calculated proportional mortality ratios (PMRs) for aortic aneurysm by county of birth and county of death, for men and women aged 45-74. Among people resident in the county of their birth, PMRs for aortic aneurysm by county ranged from 31 in Pembrokeshire to 194 in Surrey. Among 'migrants', who died in a different county from that in which they were born, PMRs by place of death varied from 85 in the group of counties which had the lowest mortality in non-migrants to 111 in those with the highest mortality in non-migrants, and PMRs by place of birth varied from 74 in counties with lowest mortality in non-migrants to 113 in those with highest mortality in non-migrants. After adjustment for place of residence at death, the relation of mortality to place of birth was highly significant statistically (P < < 0.001). These findings indicate important causes of aortic aneurysm acting early in life, perhaps related to the formation of elastin in the arterial wall.