We report the case of a woman who developed acute thrombocytopenia with hemorrhagic diathesis during adjuvant treatment of colorectal adenocarcinoma with oxaliplatin, 5-fluorouracil and leucovorin. A 55-year-old woman started adjuvant chemotherapy with oxaliplatin, 5-fluorouracil and leucovorin (mFOLFOX6). Prior to starting the 12th course of chemotherapy, a complete blood cell count showed the following values: neutrophils 1800/mm(3), platelets 136,000/m(3) and hemoglobin 11.1 g/dl. A blood count revealed that the platelet levels had dropped to 35,000/mm(3), with no significant changes in hemoglobin levels following the course. The administration of corticosteroids was begun and the platelet number was recovered. Clinicians should be aware of the possibility of oxaliplatin-induced hematological emergencies during the treatment of colorectal cancer patients in order to optimize supportive treatment and avoid toxic mortality.