The relationship between nonsteroidal anti-inflammatory drugs (NSAIDs) and deterioration of renal function was examined in a large group of hospitalized patients carefully monitored for adverse drug effects and in a large group of outpatients whose discharge diagnoses after subsequent hospital admission were recorded. In the in-hospital study, no association between the use of NSAIDs and drug-attributed elevation of serum urea nitrogen levels diagnosed during hospitalization was present. In the outpatient study, none of the patients who used NSAIDs was hospitalized for acute renal disease. The majority of the available data related to indomethacin, ibuprofen, and phenylbutazone. (JAMA 1984;251:1299-1300)