Electrolyte and renal hemodynamic imbalance, acute interstitial nephritis with nephrotic-range proteinuria, papillary necrosis, tubular necrosis, and vasculitis are complications after intake of nonsteroidal anti-inflammatory drugs (NSAID). We report on 2 cases of biopsy-proven granulomatous interstitial nephritis with rapidly progressing renal insufficiency. Patient 1 was on ketoprofen for 7 months and indomethacin for 10 weeks before admission to hospital. The medication was not discontinued and renal insufficiency progressed to end-stage renal failure. Renal function did not respond to steroid and tuberculostatic treatment. Patient 2 was on diclofenac for 6 months and indomethacin for 7 weeks before admission to hospital. These drugs were withdrawn at diagnosis and renal function rapidly improved. We conclude that granulomatous interstitial nephritis may be a complication of NSAID medication indicating a cell-mediated immunologic disorder. False diagnosis (sarcoidosis, tuberculosis) may lead to end-stage renal disease (case 1). Discontinuation of medication obviates further therapy (case 2).