Osteoarthritis (OA) and rheumatoid arthritis (RA) are among the most prevalent chronic illnesses and leading causes of disability in the United States. The clinical symptoms of OA and RA, pain and inflammation, are biologic processes mediated in part by prostanoids-prostaglandins, prostacyclin, and thromboxanes. The intermediate enzymes responsible for prostaglandin biosynthesis, cyclooxygenase (COX)-1 and COX-2, have been the target of arthritis therapy using nonselective nonsteroidal anti-inflammatory drugs (NSAIDs). An understanding of the biochemistry and molecular pharmacology of COX enzymes has allowed for the development of agents that specifically inhibit COX-2. COX-2-selective inhibitors have efficacy in OA and RA that is similar to that of NSAIDs but with a lower potential for upper gastrointestinal injury, a serious side effect of nonselective NSAIDs. COX-2-selective inhibitors have been increasingly used in the treatment of OA and RA as well as other inflammatory arthropathies including ankylosing spondylitis and gout. Clinical trials with two currently available drugs, rofecoxib and celecoxib, have demonstrated efficacy comparable to nonselective NSAIDs but with a lower risk of gastrointestinal side effects. In general, these drugs are well tolerated in patients with aspirin-sensitive asthma. Rofecoxib is well tolerated in patients with sulfonamide sensitivities; further studies are needed to fully characterize the utility of celecoxib in these patients. Clinical experience shows that because of their improved GI safety, rofecoxib and celecoxib, and newer COX-2-selective inhibitors (valdecoxib, etoricoxib, parecoxib), represent a significant advance in the treatment of arthritis and other related inflammatory conditions.