There seems to be a clear correlation between antibodies against domain I (anti-DI) of β2Glycoprotein I and severe clinical profiles in antiphospholipid syndrome (APS) patients. We investigated the clinical significance of anti-DI antibodies in a cohort of aPL carriers. One hundred and five carriers persistently positive for IgG anti-β2Glycoprotein 1 antibodies (a-β2GPI) and/or IgG anticardiolipin (aCL) and/or lupus anticoagulants (LAC) were tested for the presence of anti-DI antibodies using the QUANTA Flash® Beta2GPI-Domain I chemiluminescence immunoassay. Anti-DI antibodies were detected in 44 aPL carriers (41.9%) and they were significantly associated to triple aPL positivity (LAC plus IgG a-β2GPI plus IgG aCL antibodies). Isolated LAC and a-β2GPI antibodies were significantly associated to anti-DI negative aPL carriers. During a 82.2 month mean follow-up, ten aPL carriers (9.5%) developed a first thrombotic event so becoming APS patients. Anti-DI antibodies, triple aPL positivity, thromboembolic risk factors and autoimmune disorders significantly prevailed in carriers becoming APS. Logistic regression analysis showed that anti-DI positivity was an independent risk factor for thrombosis. Anti-DI antibody positivity can be considered a new risk factor predictive of the first thrombotic event in aPL carriers, instead, negative anti-DI may be useful to identify low-risk aPL carriers. •Anti-DomainI antibodies (aDI) have never been evaluated in antiphospholipid antibody carriers.•The clinical significance of aDI was investigated in 105 antiphospholipid antibody carriers.•ADI are an independent risk factor for thrombosis in antiphospholipid antibody carriers.•Negative aDI may be useful to identify low-risk antiphospholipid antibody carriers.