In this review it is shown that nimesulide, a selective cyclooxigenase-2 (COX-2) inhibitor, is different from other selective COX-2 inhibitors and classical non-steroidal anti-inflammatory drugs (NSAIDs). The anti-inflammatory effect mechanism of nimesulide (inhibition of inflammatory mediators) is similar to other classic NSAIDs, but the protective effect of nimesulide on classic NSAID-induced ulcers elucidates the difference between nimesulide and these other drugs. It is known that the selective COX-2 inhibitor nimesulide prevents NSAID-induced ulcers, while celecoxib and rofecoxib, which are more selective to COX-2, failed to prevent these ulcers. Nimesulide produces gastro-protective effects via a completely different mechanism. In addition, while selective COX-2 inhibitors increase the risk for cardiovascular diseases, nimesulide does not exert significant cardiotoxicity. This data suggests that gastrointestinal side effects of classic NSAIDs cannot be related to the COX-1 inhibition alone and also suggest that nimesulide is an atypical NSAID, which is different from both non-selective and selective COX-2 inhibitors.