The kidneys are organs of singular significance for the surgeon operating on the abdominal aorta. Their anatomic disposition often creates grave technical problems and their functional state has intimate relationship to diagnostic studies, case selection, and operative results. In this essay, we wish to illustrate, with a background experience of 250 cases of abdominal aortic operations, the more important of these problems and to discuss, respectively, their recognition, prevention, and management. Problems of Renal Physiology The candidates for surgical procedures on the abdominal aorta are almost always suffering from systemic arteriosclerosis, often to a severe degree. As one of the commonest organ manifestations of this disease they often have some measure of renal arteriosclerotic involvement. While this fact is not always demonstrable by clinical tests, it is well borne out by operative and postmortem observations. It is not only prudent but physiologically correct, therefore, to regard every patient with arteriosclerotic