It has become obvious that consideration of only pathological anatomy gives little insight into the pathogenesis of cystic kidney disease. Better markers are required before an adequate system of classification can be developed. Once nosologic separation has been effected, specific diseases can be studied in more detail and an attempt can be made to elucidate the fundamental molecular abnormality. Genetic factors may be extremely useful in defining discrete disease entities; unfortunately, they have been too frequently disregarded by workers in the field. If progress is to be made in the area of structural abnormalities of the kidney, the common efforts of nephrologists, pathologists, physiologists, and geneticists will be required.