A case of reversible renal failure due to sarcoid granulomatous nephritis is described. The patient, a 21-year-old student, was admitted with renal insufficiency (GFR =25 ml/min); no damage was found in any organ except for slightly enlarged pulmonary hilar lymph nodes. Repeated percutaneous renal biopsies showed an interstitial noncaseating granulomatous nephritis. Steroid therapy provided rapid improvement and the diagnosis of sarcoidosis was established. Complete recovery of renal function with normal urinalyses was seen.