Résumé : The aims of this review article were to clarify the steps that may lead to a proper diagnosis of fetal and neonatal renal cystic diseases. All the hereditary cystic diseases are reviewed and a classification is proposed. The various sonographic patterns that can be used to ascertain the diagnosis are also reviewed. Finally, tables with differential diagnoses are presented to help the reader in the work-up of such pathologies. © Springer-Verlag 2006.