Since Sternbach's first review, serotonin syndrome has been reported many times. Our purpose was to examine this concept's pertinence, utility and meaning. Its physiopathology remains unclear: 5-HT1A receptors activation is certain, but others mechanisms and individual or family factors could be also involved. Appearance circumstances are more various than first expected. The concept of serotonin syndrome seems to bring together entities that differ in physiopathology and seriousness, and we propose to distinguish between serotonin syndrome and other types of syndromes. Knowing serotonin syndrome is useful both for prevention and for recognizing it as a potentially lethal emergency.