Cystic kidneys have large bubbles of fluid that gradually enlarge and destroy the normal kidney structure. This condition can be palpated, and in a lean ferret, enlarged kidneys are visible when the animal is held up and stretched out. Often, only one kidney is affected, and when it is removed, the ferret can then live a normal life because only one kidney is necessary for survival. If both kidneys are affected, the ferret will die when there is not enough normal tissue left to maintain adequate function. Ferrets are often 2 or 3 years old when these problems are diagnosed, but occasionally cystic kidneys are found in kits soon after weaning. This is considered to be an inherited condition in ferrets.