Forty-two postoperative patients, each with demonstrable failure of two or more vital organ systems, have been studied as they define a syndrome of multiple organ failure. They typify the emerging clinical entity of patients kept alive solely by reason of specific mechanical and pharmacologic support. Trauma initiated hospitalization in 40 per cent and major bleeding, in 11 per cent. Sepsis was judged to be of etiologic significance in 69 per cent. Complications in clinical management were, in retrospect, thought to be of contributory etiologic significance in 57 per cent. Twenty-nine of 42 patients died; a mortality of 69 per cent. Mean duration of multiple organ failure was 30.5 days. Hospital cost, omitting the physician's fees, was conservatively estimated at $700 per day. Scientific, social, moral, ethical and legal factors emphasize the need to establish a statistically valid large data base concerning this new man-made syndrome which has both important scientific and social implications. This study is a first step in this direction.