Non-steroidal anti-inflammatory drugs have a wide range of use in clinical practice because of their analgesic and anti-inflammatory properties. However, their potential nephrotoxicity has been noted. The case histories were studied, retrospectively, in 13 patients who were taking non-steroidal anti-inflammatory drugs as follows: four on fenoprofen (Nalfon), three on naproxen (Naprosyn), two on ibuprofen (Motrin), two on sulindac (Clinoril), one on tolmetin (Tolectin), and one on indomethacin (Indocin) and who exhibited abnormal urinalysis or a deterioration in renal function. Nine of the patients underwent renal biopsies, and eight of these biopsies were positive for interstitial nephritis. In addition to the presentation of additional cases of non-steroidal anti-inflammatory drug nephrotoxicity, a brief review of the current theories of the nephrotoxic mechanism is presented.