An adult Holstein cow, six days in milk, presented with her calf to the Cornell University Farm Animal Hospital for toxic mastitis and hypocalcemia. On presentation the patient showed signs of shock, mastitis, and hemostatic disorder. She had oral mucosal petechiation, hyperemic and chemotic conjunctiva, frank blood flowing from her cervix, bruising on her vulva and perineum, and melena. Her right jugular vein was severely thrombosed, and she bled excessively upon venipuncture and intravenous catheter placement. Blood work revealed severe thrombocytopenia, moderate anemia, left shift with toxic changes, elevated PT, low fibrinogen, and increased D-dimers. Thromboelastography confirmed markedly weak fibrin formation. Escherichia coli was isolated from her left mammary gland. The patient was treated aggressively with antibiotic therapy, intravenous fluids, blood transfusion, and supportive care over three weeks before recovering from overt disseminated intravascular coagulation and being discharged to her owners.