Surya Seshan, MBBS, of New York-Presbyterian Hospital and Weill Cornell Medical College, discusses the basics of antiphospholipid antibody syndrome, first described by Professor Hughes in the 1980s. The syndrome is characterized by recurrent vascular thrombosis and is often associated with other autoimmune diseases. An international consensus in 1999 developed certain criteria for diagnosis of the syndrome, which includes an event of vascular thrombosis or pregnancy morbidity and loss, along with positive serologies.