Although nonsteroidal anti-inflammatory drugs (NSAIDs) effectively treat a variety of inflammatory diseases, these agents may cause deleterious effects on kidney function, especially with respect to solute homeostasis and maintenance of renal perfusion and glomerular filtration. NSAIDs act by reducing prostaglandin biosynthesis through inhibition of cyclooxygenase (COX) which exists as two isoforms (COX-1 and COX-2). NSAID-induced gastrointestinal toxicity is generally believed to occur through blockade of COX-1 activity, whereas the anti-inflammatory effects of NSAIDs are thought to occur primarily through inhibition of the inducible isoform, COX-2. However, the situation in the kidney may be somewhat different. Recent studies have demonstrated that COX-2 is constitutively expressed in renal tissues of all species; this isoform may, therefore, be intimately involved in prostaglandin-dependent renal homeostatic processes. Drugs that selectively inhibit COX-2 might, therefore, be expected to produce effects on renal function similar to nonselective NSAIDs which inhibit both COX-1 and COX-2. This assertion is borne out by recent clinical studies showing that the COX-2 inhibitors rofecoxib and celecoxib procedure qualitative changes in urinary prostaglandin excretion, glomerular filtration rate, sodium retention, and their consequences similar to nonselective NSAIDs. It, therefore, seems unlikely that these COX-2 inhibitors (and perhaps their successors) will offer renal safety benefits over nonselective NSAID therapies, and, at this juncture, it is reasonable to assume that all NSAIDs, including COX-2-selective inhibitors, share a similar risk for adverse renal effects.