Recent interest in recasting our knowledge of the kidney has included, among other things, a study of tumors of the kidney, and special attention has been given to the histogenesis of renal neoplasms. Various articles have been contributed to the medical literature with suggested classifications and origins of these growths; but, so far, no uniformity of opinion has been reached. However, most of the investigators have agreed that tumors of the kidney are grouped into three general types: (1) tumors of the capsule; (2) tumors of the cortex, and (3) tumors of the pelvis and collecting tubules. When we come to the origin of these tumors, a perusal of the literature shows how confusing the whole question is, with reference not only to tumors of different types but also with those of the same type. Our purpose in this paper is to report a tumor that definitely falls into the