This study aimed to evaluate the benefits of reducing dietary phosphorus in cats with renal failure. Cats with reduced renal mass were fed either a normal phosphorus diet or a restricted phosphors diet for up to 343 days. Renal function was checked biweekly using blood urea nitrogen, plasma creatinine and inulin clearance procedures. Results showed that neither diet caused any significant change in renal function during the test period. However, histological examination of kidneys of cats obtained at post mortem clearly demarcated cats in the 2 groups. Cats fed the normal phosphorus diet had mineralisation, fibrosis and mononuclear cell infiltration of their kidneys whereas cats fed restricted phosphorus had minimal or no pathological renal changes.