Among all inherited cystic kidney diseases, the commonest are polycystic kidney diseases, which include 2 diseases characterized by their pathological characteristics and their mode of inheritance, namely autosomal dominant or recessive. Autosomal dominant polycystic kidney disease is usually diagnosed in adulthood and is related at least to 2 different genes; PKD1 gene on chromosome 16 accounts for 85% of cases. This frequent disease (1 in 1,000 people) leads to end-stage renal failure in most patients at a mean age of 55 years. Renal ultrasonography allows its detection at an early stage, during childhood or adolescence, and even in utero in some cases. Autosomal recessive polycystic kidney disease, related to a single gene mapped to chromosome 6, is a rare disease, usually diagnosed during infancy because of enlarged kidneys and hypertension. The early occurrence of advanced renal failure is uncommon and only 1/3 of patients require renal replacement therapy during childhood. The term "polycystic kidney disease" should be limited to these 2 diseases; however there are many other inherited conditions including renal cysts like tuberous sclerosis or Hippel-Lindau's disease in adults, and several malformative syndromes in children.