Although cimetidine causes a transient rise in serum creatinine without reduction of renal function, acute renal failure due to acute interstitial nephritis is rare in patients after cimetidine treatment. We here present a case of acute renal failure and acute interstitial nephritis that occurred during cimetidine treatment. A 38-year old woman was referred to our hospital because of nausea and general weakness. She had been taking cimetidine for 3 weeks because of epigasric discomfort. On admission, serum creatinine was 3.9 mg/dL and urinalysis showed mild proteinuria and hematuria. There was no history of pyelonephritis, diabetes mellitus, hypertension, toxin exposure. Renal biopsy showed severe interstitial infiltration of lymphocytes without definite glomerular change. After withdrawal of cimetidine, renal function completely recovered. (Korean. J. Med 57:941-945, 1999)