[Unilateral renal cystic disease].

Unilateral and localized cystic disease of the kidney, is characterized by the substitution of either all or a portion of one of the kidneys, by no encapsulated, multiple simple cysts. We present a case--to our knowledge the first in the Spanish bibliography-, of this rare benign condition that needs to be recognized to be differentiated from more transcendent ones. Contrary to autosomal dominant polycystic kidney disease, it is unilateral, it is not familiar, and it is neither progressive nor associated with renal insufficiency or with cysts in other abdominal organs. Lack of encapsulation allows, in general, to distinguish it from multilocular cystic nephroma and cystic renal carcinoma.