Guillain-Barré syndrome, or acute inflammatory demyelinating polyradiculoneuropathy, and immune thrombocytopenic purpura are both autoimmune disorders thought to result from molecular mimicry in response to an antecedent introduction of foreign antigen. Guillain-Barré syndrome is an ascending motor paralysis that can lead to respiratory compromise. Immune thrombocytopenic purpura is an isolated disorder of platelet destruction leading to mucocutaneous bleeding. Guillain-Barré does not typically occur with other autoimmune disorders, and concurrent Guillain-Barré and immune thrombocytopenic purpura has only rarely been reported. We present a patient with both conditions who experienced prompt resolution of neurologic and hematologic sequelae after intravenous immunoglobulin therapy was initiated within 12 hours of presentation. The case provides further evidence that Guillain-Barré syndrome and immune thrombocytopenic purpura can occur simultaneously, possibly caused by a similar pathogenic mechanism, as well as suggesting that the prompt initiation of intravenous immunoglobulin is an effective monotherapy leading to prompt resolution of both conditions and prevention of further sequelae. © 2006 Elsevier Inc. All rights reserved.