The 'catastrophic' variant of the antiphospholipid syndrome (APS) is characterized by a diffuse thrombotic microvasculopathy. In contrast to the classical APS, single venous or arterial medium-to-large blood vessel occlusions are uncommon. The mechanisms of catastrophic APS are not clearly understood. In addition, there are no studies on pathophysiologic mechanisms of catastrophic APS. The clinical manifestations of catastrophic APS probably depend on (a) the organs affected by the thrombotic events and extent of the thrombosis and (b) manifestations of the systemic inflammatory response syndrome which are presumed to be due to excessive cytokine release from affected and necrotic tissues. The evident relationship between APS and infection may enable us to explain the development of catastrophic APS using the sepsis model. This is because catastrophic APS is characterized by multiple microvascular thrombotic events, of rapid onset, and causing multiorgan failure, a picture suggestive of septic shock, in which, there is a massive, acute inflammatory response.