Multiple organ dysfunction syndrome (MODS) is a clinical situation that has been described as a result of the rapid progress and advances that have been made in recent decades in the physiology, diagnosis, and therapeutic support of critically ill patients. In 1991, in view of the confusing terminology used to characterize processes coursing with systemic inflammatory response syndrome (SIRS), a consensus conference was held. A series of basic definitions were established and the term "multiple organ failure" was replace by MODS. In response to outside aggression, the organism tries to defend itself with two mechanisms: a non-specific humoral and cellular response called inflammation, and a specific antigenic response that modifies the genetic codes of cells of the defense system and constitutes an immunological response. At present it is thought that the inflammatory response is activated (SIRS) in response to an uncontrolled aggression, but an antiinflammatory response syndrome (ARS) exists as well. An exaggerated SIRS can lead to MODS. MODS usually debuts with pulmonary dysfunction. If the aggression persists, cardiovascular, renal, hepatic, coagulation, central nervous system, gastrointestinal metabolism, neuroendocrine and musculoskeletal failure follow. A series of causes often trigger this syndrome and certain factors favor it. Prevention of these causes and factors in fundamental for controlling the occurrence of MODS. At present, there is no clear treatment for MODS, although numerous studies designed to block the release of certain proinflammatory mediators or to neutralize antiinflammatory responses are being carried out.