Nonsteroidal anti-inflammatory drugs (NSAIDs) are widely used. These agents are associated with adverse renal effects caused by the reduction in synthesis of renal prostaglandins through inhibition of cyclooxygenase (COX). Both isoforms of COX, COX-1 and COX-2, are expressed in the kidney in constitutive and inducible forms. It is assumed therefore that the COX-2-selective inhibitors, rofecoxib and celecoxib, would have an effect on renal function similar to that of nonselective NSAIDs. Several studies have evaluated this issue, although they have different study models and some have design flaws that limit their interpretation. Therefore, conclusions should be based on the pattern of observed effects rather than on individual data. These studies suggest that both celecoxib and rofecoxib can cause sodium retention and decrease glomerular filtration rate (GFR) to a similar extent as nonselective NSAIDs in patients at risk for adverse renal effects. Consequently, the same precautions regarding renal risk that are followed for nonselective NSAIDs should be used when selective COX-2 inhibitors are administered.