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 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. Currently, it documents the entire clinical, laboratory, and therapeutic data of more than 300 patients whose data have been fully registered. This registry can be freely consulted at the Internet (www.med.ub.es/MIMMUN/FORUM/CAPS.HTM) and it is expected that the periodical analysis of these data will allow us to increase our knowledge of this condition.