Despite recent advances in diagnosis and care of critically ill patients sepsis related mortality rate remains unacceptably high. Therefore, new methods of evaluation are necessary to provide an earlier and more accurate characterization of septic patients. Based on the (oncologic) TNM system, the PIRO concept was introduced as a new staging system for sepsis in order to assess risk and predict prognosis, with potential to assist in inclusion of patients in clinical studies and estimate the probability of response of patients to specific therapeutic interventions.