Longstanding scoliosis of the lumbar spine with convexity to the left leads to severe atherosclerosis in the adjacent segment of the abdominal aorta. By contrast, the lateral wall of the ascending aorta, which is free to pulsate, usually is not affected even in very old persons. This relative immunity, however, is not maintained in cases of syphilitic mesaortitis; damage to the elastic tissues of the media leads to atherosclerosis. Man is the only mammal known to be highly susceptible to severe atherosclerosis. The concept is advanced that the erect posture of man, which leads to the physiologic anterior curvature of the lumbar spine, predisposes to atheroma formation in the abdominal aorta, particularly in women. Evidence for the osteoporosis-atherosclerosis concept is presented. Sustained muscular activity starting early in life can delay osteoporosis and atherosclerosis. A possible mechanism for the onset and gradual progression of physiologic osteoporosis is suggested. The concept of atherogenesis advanced here is based on observations which suggest a correlation of aging processes in the mesenchymal tissues. These aging processes, in conjunction with mechanical factors partly caused by the erect posture, may account for the unique susceptibility of man to severe atherosclerosis.