BACKGROUND: Celecoxib and rofecoxib have been used in Norway since 2000. These cyclooxygenase 2 inhibitors (COX-2 inhibitors) have no better clinical efficacy than older non-steroid anti-inflammatory drugs (NSAIDs) in the treatment of rheumatoid arthritis or osteoarthritis, but may possibly lead to a lower incidence of upper gastrointestinal ulcers. MATERIAL AND METHODS: Published and unpublished clinical data on side effects were examined and interpreted. The aim was to evaluate the general safety of these new drugs compared with older NSAIDs. RESULTS: The incidence of side effects is addressed in two large published studies comparing COX-2 inhibitors with other NSAIDs. Only rofecoxib showed an unequivocal lower incidence of complicated upper gastrointestinal ulcers. However, the incidence of serious side effects was significantly higher in the rofecoxib group. In the other study there was a trend towards more serious side effects in the celecoxib group. INTERPRETATION: The available clinical data do not suggest that COX-2 inhibitors are safer drugs than other NSAIDs.