Acquired Glanzmann's thrombasthenia is an uncommon event in association with leukemia. The authors describe a patient with acute lymphoblastic leukemia (ALL) who presented with severe hemorrhagic syndrome, without disseminated intravascular coagulation. The patient's course was complicated by the occurrence of severe hemorrhagic episodes, with a thrombasthenia-like profile, requiring multiple transfusions with packed red cells, platelets, and fresh-frozen plasma. Biological explorations detected anti-GPIIb/IIIa complex antibodies. The patient finally died with refractory disease and persistent bleeding. This case is the first reported of autoantibodies to GPIIb/IIIa in ALL. Such paraneoplastic syndrome is potentially responsible for severe life-threatening hemorrhage.