A 5 year old Quarter Horse gelding presented to the Cornell University Equine Hospital with a 1.5 month history of chronic renal failure. Beginning at approximately 9 months of age, the gelding had been polyuric, and began exhibiting clinical signs of renal failure 1.5 months prior to presentation, including dramatic weight loss, inappetance, and azotemia. The problem list included: polyuria/polydipsia, inappetance, weight loss, cachexia, severe azotemia, uremia (dental tartar, uremic odor), hypovolemia, electrolyte abnormalities (hyponatremia, hypercalcemia), isosthenuria, proteinuria, and a small fibrotic appearing right kidney on ultrasound (left not visualized). Post-mortem, there was diffuse, chronic, severe bilateral renal fibrosis with unilateral renal calculi in the left kidney. Histologically, the kidneys contained evidence of primitive mesenchyme and tubules. Due to the history, structural, and histological changes, a diagnosis of renal dysplasia leading to chronic renal failure, interstitial nephritis, pyelonephritis, and ureterolithiasis was made.