Antiphospholipid syndrome (APS) is an autoimmune disease characterized by recurrent arterial or venous thrombosis or fetal loss and the presence of antiphospholipid antibodies (aPL). Genetic factors are thought to play a role in the susceptibility to APS. Similar to many other polygenic autoimmune diseases, human leukocyte antigen associations have been reported. The genetics of b(2)-glycoprotein I, one of the most representative target antigens of aPL, has been extensively studied. Additional genetic risk factors for the development of thrombosis in patients with aPL have also been discussed. However, the genes involved in APS have not been identified because antigen specificity of aPL and the pathophysiology of APS are highly heterogeneous and multifactorial. Genome-wide linkage analysis and larger cohort studies would lead to better understanding of the genes that might be involved in APS.