Background: Polycystic kidney disease (PKD) is an inherited disorder with an autosomal dominant pattern. This disease is most commonly seen in Persian cats and related breeds and leads to the formation of multiple fluid-filled cysts within the renal tissue. PKD gradually impairs kidney function and, in severe cases, can result in renal failure. Since clinical signs usually appear in middle age, case reports emphasize the importance of early screening and supportive care. Methods: In June ۲۰۲۵, a four-year-old male Persian cat was referred to a veterinary diagnostic center. According to the owner, the cat presented clinical signs including lethargy, hypodipsia, ptyalism, and stomatitis. After a complete clinical examination, blood samples were collected for serum biochemical analysis (BUN, creatinine, phosphorus, albumin), and a full abdominal ultrasonography was performed by a radiology and ultrasound specialist. Results: Laboratory findings revealed a marked increase in BUN (۳۷۵ mg/dL), creatinine (۶.۴۶ mg/dL), and phosphorus (۱۳.۳ mg/dL), consistent with stage ۴ chronic kidney disease. Ultrasonographic evaluation demonstrated bilateral renomegaly with irregular margins and multiple thin-walled anechoic cysts throughout the cortical and medullary regions of the kidneys. The largest cysts measured ۳.۵ × ۲.۹۷ cm (right kidney) and ۳.۱ × ۳ cm (left kidney). Structural changes, including cortical thinning and displacement of the renal pelvis, were evident. The clinical signs were consistent with laboratory and imaging findings, confirming advanced renal dysfunction. Conclusion: This case report illustrates the early onset of advanced polycystic kidney disease in a Persian cat. Regular ultrasonographic screening of predisposed breeds is essential for timely detection of the disease. Although no definitive treatment exists, supportive management including correction of metabolic imbalances, dietary adjustment, and symptomatic therapy plays a pivotal role in improving quality of life and survival. Moreover, raising awareness among breeders and owners about the hereditary nature of this disease is crucial.