In the multicystical renal dysplasia we have to do with a congenital malformation due to a developmental disturbance of the bud of the ureter. It is characterized by a conglomerate of cysts, rarely by a single cyst without a functioning renal parenchyma, atresia or complete absence of the ureter belonging to this as well as hypoplasia or atresia of the vascular stump. In childhood the clinical picture is not observed frequently, in adult persons only rarely. Though the case in question is a homogeneous disturbance of the development, in childhood and adult age pretty different findings are the result. In childhood in most cases a palpable tumour caused by a multicystical kidney is to be found, in adult persons often a more distinct formation of a defect occurs, particularly of the ureter as well as a nearly obligate calcification of the walls of the cyst. Often the clinical picture is to be found in combination with other, above all urological congenital anomalies. Two own observations of multicystical renal dysplasia in adult age are reported and in connection with 33 cases of literature they are comparatively investigated.