The classification of cystic kidney diseases according to the pathologic-anatomic potter classification may be difficult. New molecular genetic findings are important to understand the underlying pathogenesis, but less useful to classify the hereditary diseases. An exact classification of polycystic kidney disease in fetus and children is very important for the human genetic consultation. Therefore, the investigation of pathological anatomy of kidney and liver, as well as the evaluation of additional malformations and family history is necessary. For clinical use the mode of inheritance (autosomal dominant and autosomal recessive) is used to differentiate hereditary polycystic kidney diseases.