This article reviews the basic epidemiologic and prognostic data for the syndrome of MSOF. When MSOF is defined as severe physiologic abnormalities, it occurs following a wide variety of diseases. The distinguishing feature of MSOF appears not to be the underlying etiology, but the uniform and frequently fatal outcome once it develops. This suggests that MSOF may represent a final common pathway to death rather than a clinical syndrome with a single underlying etiology. Regardless of cause, evaluating the incremental impact of new therapy on MSOF will be assisted by the adoption of uniform definitions as well as by the explicit measurement of severity of disease and calculation of individual probabilities of death.