Scoring systems which try to quantify patient risk are becoming increasingly popular. They have been widely used in intensive care unit patients, trauma patients, and patients undergoing operation. Both general scores, such as APACHE and POSSUM, and specific scores, such as the Detsky Index for post-operative cardiac morbidity and mortality, have been defined. They can be used for comparative audit, to define treatment options, to predict long- and short-term outcome, and to define morbidity and mortality associated with a specific condition. Little evidence yet exists that it is possible to move patients from higher to lower risk groups and thus lower post-operative mortality. However, this may be achieved in time. All surgeons need to be involved in further refinements of scoring systems.