Polycystic kidney disease is a relatively common inherited disease in some pedigreed breeds. Signs of this disease are not often seen until later in life. In many breeding programs, affected or carrier cats are used for breeding before clinical signs have appeared. Ultrasound screening is currently available to screen breeding cats, but there is a need for a highly reliable and cost-effective test. Finding the genetic mutation that causes PKD will allow DNA testing to identify cats carrying the gene before they are used in a breeding program. Through the examination of DNA samples already collected by the researcher, a mutation that is highly likely to be responsible for feline PKD has been identified. This phase of the research was partially funded by the Winn Feline Foundation. Work must now be carried out to confirm the responsible mutation and develop a simple genetic test for PKD.