Diclofenac sodium, a phenylacetic acid derivative, is a non-steroidal, anti-inflammatory, analgesic agent advocated for use in rheumatoid arthritis, degenerative joint disease, ankylosing spondylitis and allied conditions, and in the treatment of pain resulting from minor surgery, trauma and dysmenorrhoea. Published data indicate that diclofenac 75 to 150mg daily (25 to 50mg 3 times daily) is comparable in efficacy with ordinary aspirin 3 to 5g daily and indomethacin 75 to 150mg daily in rheumatoid arthritis and with indomethacin in osteoarthritis. Available data suggest that in patients with osteoarthritis diclofenac sodium is comparable in efficacy and tolerability with naproxen, ibuprofen, sulindac and diflunisal. As oral diclofenac is generally given in 3 divided daily doses it may be at a disadvantage relative to less frequent administration with naproxen, diflunisal and sulindac in rheumatoid arthritis, although there is some evidence of diclofenac's efficacy when administered twice daily, or once daily as a slow release tablet. The drug is also available as suppositories and ampoules for intramuscular injection. No one of the non-steroidal anti-inflammatory agents is the most suitable drug for all patients requiring such therapy, and diclofenac should be considered along with other drugs of its type in the arthritic patient.