Although less than 1% of patients with the antiphospholipid syndrome (APS) develop the catastrophic variant, its potentially lethal outcome emphasizes its importance in clinical medicine today. However, the rarity of this variant makes it extraordinarily difficult to study in any systematic way. In order to put together all of the published case reports as well as the new diagnosed cases from all over the world, an international registry of patients with catastrophic APS (CAPS Registry) was created in 2000 by the European Forum on Antiphospholipid Antibodies (see http://www.med.ub.es/MIMMUN/FORUM/CAPS.HTM). Currently, it documents the entire clinical, laboratory and therapeutic data of more than 300 patients whose data has been fully registered.