Charles Pratt said - >I know from experience with humans that simple renal cysts are fairly >common and are a benign condition. What you're describing sounds like >polycystic kidney... Charles, you're right on the mark here. Single renal cysts are extremely common in ferrets - about 20% of ferrets have them, and they don't cause any problem at all. However, rarely in ferrets, as in most animal species, individuals may be born with polycystic kidneys, which are so full of these little cysts that the kidneys cannot filtre the blood properly, and uremia ensues. It is a congenital defect in which the glomerular (filtering) portion of the kidney does not join with the tubular (or plumbing) part of the kidneys. The kidneys are for the large part non-functional, and the animal generally dies before the age of 1 year ( they almost always have some functional kidney tissue, so they live a little while. Now I've got to go back and find the context of this question/comment.... Bruce Williams, DVM, DACVP Dept. of Vet Path, AFIP [log in to unmask] OR Chief Pathologist, AccuPath [log in to unmask] [Posted in FML issue 1389]