We report the case of a white woman with insulin-dependent diabetes for 12 years who had rapid deterioration in renal function over a 7-month period. A renal biopsy showed widespread deposition of a polarizing crystalline material consistent with calcium oxalate. Fat malabsorption due to diabetic diarrhea was first documented 5 years earlier when renal function was normal. Chronic malabsorption can lead to chronic interstitial nephritis secondary to oxalate deposition, but rarely leads to acute deterioration in renal function. This entity should be considered in individuals with steatorrhea and no other cause for their renal failure. © 1995.