Prolonged ingestion of mixed analgesics containing phenacetin has been associated significantly with the development of a chronic interstitial nephritis frequently associated with papillary necrosis. This disease is frequently underdiagnosed. If an adequate history of headache and/or backache (of which most of these patients complain) is not taken, the central causative effect of phenacetin ingestion may never be appreciated. Laboratory tests show the usual abnormalities seen in any form of chronic interstitial nephritis such as poor urinary concentration, renal failure with large urine output, and no hypertension. Papillary necrosis is helpful but not pathognomonic. The type of medications ingested appears to be changing to prescription compounds. The with significant improvement in renal function.