A few years ago, during work on a series of experiments on the renal veins, it was observed that marked hemorrhage was frequently associated with venous obstruction of the kidney. In several instances a large perirenal hematoma followed complete ligation of the renal vein. Subcapsular and parenchymal hemorrhages were present constantly in the large, tense, congested kidneys. It occurred to us that certain cases of spontaneous nontraumatic perirenal hematomas in man might find an explanation in venous congestion of the kidneys, with the resultant elevated vascular pressures and possible capsular ruptures. We divided our investigations into three kinds of research: (1) the clinical study of a personal case, (2) the experimental ligature of the renal veins in animals and (3) the etiologic study of cases collected from the world's literature. We believe that elevation of intracapsular and vascular pressure in the kidney can, and probably frequently does, produce spontaneous hemorrhages