The most prevalent inherited genetic disease in cats is polycystic kidney disease (PKD). Persian and Persian-related breeds are predominantly affected with a reported 40-50% of Persians worldwide in these numbers. The purpose of this study was to demonstrate the repeatability of ultrasound scanning in the detection of PKD and to assess the progression of the disease over time. Diagnosis of PKD relied on ultrasound scanning until the development of the PKD genetic test. But genetic testing has the limitations of only detecting the autosomal dominant form of PKD and not other forms of cystic kidney disease. As well, genetic testing is unable to assess the severity of the disease. The study demonstrated 100% repeatability of ultrasound scanning in the diagnosis of PKD. Of the small number of PKD positive cats re-scanned after one year, 75% showed progression of the disease. The authors stated that ultrasound scanning at 10 months of age with a high resolution probe and experienced ultrasonographer is a reliable method of PKD diagnosis. [VT]