Polycystic kidney disease (PKD) is a cystic genetic disorder of the kidneys which is typically associated with cystic bile duct dilatation in the liver in humans, and domestic and laboratory animals. In humans, there are two types of PKD, autosomal dominant polycystic kidney disease (ADPKD) and autosomal recessive polycystic kidney disease (ARPKD). ADPKD is caused by mutations in PKD1 or PKD2 gene while ARPKD is caused by mutation or loss of the PKHD1 (polycystic kidney and hepatic disease 1) gene. Here we report a morphologically confirmed case of spontaneous PKD in a Sprague-Dawley rat in which anatomic pathology examination revealed numerous cystic changes in the kidney and liver. Lesions consisted of marked cystic dilatations of renal tubules, and moderate cystic dilatations of intrahepatic bile ducts with portal fibrosis. We present detailed histologic features of the spontaneous PKD and compare them with disease model rats carrying an autosomal recessive PKHD 1 gene mutation.