—Geisinger1 stated that supernumerary kidney has remained so rare that its discovery has been carefully recorded in most instances and has led to several diligent consultations of records. Thirty-eight cases of true supernumerary kidney, reasonably authenticated, are reported in the world's literature. To this number Geisinger added 2 cases, bringing the total to 40.The accessory organ may be equal in size, and presumably in function, to its mate. In an occasional instance it has been larger; usually it is smaller and occupies a functional status equivalent to that of the ordinary hypoplastic kidney. Not infrequently the histologic detail may be considerably disordered; more generally it is comparable to that of the normal kidney. The vascular distribution varies to an extent that makes it profitless to attempt any description. The relationship of the associated ureters is more particular and more interesting and also of more practical consequence.