Sepsis is a medical condition in which the immune system goes into overdrive, releasing chemicals into the blood to combat infection (microbes in the blood, urine, lungs, skin, or other tissues) that trigger widespread inflammation (cellular injury in body tissues). If the body is not able to regulate this immune response, it then overwhelms normal blood processes. The first mention of the word sepsis in a medical context was more than 2700 years ago in the poems of Homer. The word derives from the Greek word sepein, meaning "to rot." Sepsis occurs in 1% to 2% of all hospitalizations in the United States, affecting at least 750 000 persons and costing $17 billion per year to treat. A term sometimes used for sepsis is "blood poisoning," but there is no poison involved in sepsis. The October 27, 2010, issue of JAMA includes an article about cognitive impairment and disability among survivors of severe sepsis. This Patient Page is based on one previously published in the February 24, 2010, issue of JAMA.