The kidney is one of the most common sites of cyst. Since cystic disease of the kidney includes various disorders, it is difficult to classify the diseases systematically. It appears that the classification of the American Academy of Pediatrics is suitable for clinical side for the present. In this paper the cystic disease of the kidney is explained on actual cases. Recently, development of imaging diagnosis is contributing widely to the diagnosis of the diseases. Treatment of the diseases, however, is not established satisfactorily. It is hoped that the mechanism of occurrence of the diseases is known further and that regulation of the classification and establishment of the treatment will become available.