Whether a genetic predisposition to develop the antiphospholipid syndrome (APS) and to produce anticardiolipin antibodies (aCL) and lupus anticoagulant (LAC) exists has been addressed by family studies and by population studies on primary APS and on aCL in diseases other than primary APS. Various studies suggest a familial occurrence of aCL and LAC, with or without clinical evidence of APS. This familial tendency could be genetically determined, because APS, aCL, and LAC occur in families carrying haplotypes which contain HLA-DR4, -DR7, and -DRw53. Population studies on primary APS also indicate that HLA genes have a role in conferring susceptibility to develop primary APS. Again, DR4, DR7, and DRw53 are the relevant loci. Population studies on aCL in diseases other than primary APS indicate that aCL are associated with DR4, DR7, and DRw53, at least when they are found in patients with systemic lupus erythematosus. Because HLA-DR4, -DR7, and -DRw53 are in linkage disequilibrium, the genetic association of aCL could be with DRw53 and, depending on the regional frequency of DR4 or DR7, it could be linked with either DR4 or DR7. HLA-DR4 seems to be more important in Anglo-Saxons, whereas DR7 emerges in populations of Latin origin. In this report we review our studies and the pertinent literature in this field.