Immunization against the platelet αIIbβ3 glycoprotein due to blood transfusion represents one of the most severe complications in Glanzmann thrombasthenia (GT) disease. Anti-αIIbβ3 isoantibodies development may lead to ineffective platelet transfusion and can, in case of pregnancy, cross the placenta leading to fetal thrombocytopenia. We describe here the case of a girl with type I GT who developed high rates of anti-αIIbβ3 isoantibodies after first and unique blood transfusion. Surprisingly, this patient had only received red blood cell concentrates and immunization was presumably stimulated by the residual presence of platelets in concentrates. This study emphasizes the need for regular anti-αIIbβ3 antibodies screening in GT, even though patients have never been previously transfused with platelet concentrates.