Severity scoring systems were first introduced to intensive care units (ICUs) in 1980. The basis for their development was the intention to provide information on the prognosis of patients, the efficacy of therapeutic interventions, stratification for clinical studies, workload and benchmarking of ICUs. Despite the appearance of several specialized scoring systems, the general mortality prediction systems such as APACHE, SAPS and MPM scores and their constantly improved successors have become the most popular and widely tested models. The newest development in this field is SAPS III which is the first 'global' model using a data set acquired from 307 ICUs from all over the world.