Systems that place a numerical score on disease severity are widely used in human medicine, 1–4 and are beginning to be created and studied in veterinary medicine. In the emergency room and ICU, a variety of systems are available that potentially have multiple purposes. Some are used to globally classify the degree of physiologic derangement in any critically ill animal regardless of the diagnosis; others are designed for application to specific situations, for example trauma. These systems give us a method to objectively classify the severity of disease, in other words, predict the outcome of survival or mortality.