The diagnosis of seronegative antiphospholipid syndrome (APS) has been proposed for patients with well-defined clinical APS but persistently negative for the routinely tested antiphospholipid antibodies (aPLs): antibodies to cardiolipin (aCL) and to β(2) glycoprotein I (aβ(2)GPI) and lupus anticoagulant (LA). Antibodies directed to phosphatidylethanolamine (aPE) have been described as the sole aPLs in some patients with clinical manifestations of APS. Here, we briefly summarize the available data on the clinical associations of aPEs and propose their investigation in patients with a clinical profile highly suggestive of seronegative APS.