The serotonin syndrome is a clinical condition associated with serotonin agonists. Is due to an overstimulation of central and peripheral serotonin receptors that leads to mental, autonomic and neuromuscular changes. Usually the disorder resolves within the first 24 hours after the medications are discontinued, however some patients progress to a multiple organ failure and die. We describe four elderly patients that presented with the classic triad. They presented the symptoms in average at the third day after the initiation or variation of the treatment with serotonin reuptake inhibitors. All had a favorable response with the suspension of medications and, in three cases, with the treatment with chlorpromazine. We believe it is a potentially fatal but reversible condition, probably underdiagnosed that requires a high index of suspicion.