Chronic renal failure was observed in 10 young adult client-owned cats that had been fed 1 commercial cat food exclusively since weaning. The diet contained 40% protein and 0.32% potassium on a dry matter basis, and phosphoric acid was added during production. We attempted to determine whether exclusive feeding of this diet would induce clinical and laboratory evidence of renal dysfunction in clinically normal adult cats. Over a 2-year study, 3 of 9 of these cats developed clinical and laboratory evidence of renal dysfunction and renal lesions. Two additional cats developed renal lesions, but had normal laboratory values. The renal lesions consisted of lymphoplasmacytic interstitial nephritis and interstitial fibrosis. We concluded that chronic renal disease may develop in clinically normal adult cats fed diets high in protein and acid content, but marginally replete in potassium.