Oxaliplatin is a platinum salt that is particularly effective for treating gastrointestinal tumors. However, some reports state that oxaliplatin-based chemotherapy triggers fatal thrombocytopenia. Myelosuppression is recognized as the main cause of oxaliplatin-related thrombocytopenia, and other mechanisms for this side effect have been suggested, including splenic sequestration of platelets related to oxaliplatin-induced liver damage and immune thrombocytopenia. Other causes of thrombocytopenia such as thrombotic thrombocytopenic purpura, immune thrombocytopenic purpura, heparin-induced thrombocytopenia, and pseudothrombocytopenia should also be considered. We encountered 3 patients who developed fatal thrombocytopenia after oxaliplatin-based chemotherapy and describe the differential diagnosis of fatal thrombocytopenia here.