Vancomycin was used to treat a patient with Staphylococcus aureus endocarditis. After 3 weeks of therapy, the patient developed a diffuse maculopapular rash, which resolved upon stopping the drug. Rechallenge with vancomycin several days later resulted in reappearance of the rash and rapid onset of acute anuric renal failure. Renal biopsy revealed acute granulomatous interstitial nephritis. This is the first report of biopsy-proven vancomycin-induced acute interstitial nephritis. Renal function should be monitored closely in patients receiving vancomycin therapy.