Sepsis and septic shock are the most frequent cause of mortality in non cardiologic intensive care units. Mortality of the severe form is still elevated in spite of the progress in the antibiotic therapy and in the hemodynamic and respiratory support. The most frequent cause of death is the Multi Organ Dysfunction Syndrome (MODS). The excessive inflammatory reaction and the damage of the microvascular bed secondary to the inflammation and to the disseminated intravascular coagulation (DIC) are important pathogenetic factors. In the sepsis a complex system of cellular activation initiates the release and the interaction of activators and inhibitors of the inflammation (cytokines), the activation of the enzymatic cascade systems (coagulation, fibrinolytic and complement systems) and the synthesis of proteases and anti proteases. The activation of the coagulation system, uncontrolled by the fibrinolytic system with formation of fibrin in the micro vascular bed, has an important role in the MODS. Experimental data and clinical observations suggest a possible therapeutic role of antithrombin III (AT) in sepsis; its plasma concentration is constantly decreased in patients with sepsis or septic shock and the entity of the decrease is correlated with the severity of the clinical picture and the outcome. At has a double function: regulation of the coagulation system and anti inflammatory properties. The anti inflammatory properties depend in part on the binding to the glycosaminoglycans of the endothelial cells and the consequent release of prostacyclin (PGI2). The anti inflammatory effect is independent from the anticoagulant one. The preliminary studies on the clinical use of AT were carried out in small groups of patients with DIC associated with pathologies of different etiology and often in very critical conditions. In general the evaluation criteria were the improvement or the normalization of the laboratory data. The interpretation of the therapeutic effect of AT is difficult because the dysomogeneity of these studies. The effect on mortality is controversial. Recently three prospective, randomized, double blind studies have been published in patients with severe sepsis and septic shock. The results of the single studies are inconclusive but the limited number of patients included in each study may explain the results. A meta-analysis of the data referring to the patients with severe sepsis and septic shock evidenced an odd ratio (OR) of 0.43 with 95% confidential interval of 0.20-0.92 (p = 0.029). The preliminary analysis of the results of a phase III study is unconclusive. Time, dosage and duration of treatment are still open to question. In perspective AT may be used in other clinical conditions associated with activation of the hemostatic system (cardiac surgery, stem cell transplantation, burns) even though the preliminary results must be confirmed by prospective studies. All these data suggest severe sepsis and septic shock as main criteria for treatment.