A 64-year-old woman came to the emergency room complaining of vomiting and abdominal pain; appendicitis was suspected and surgery ordered. A blood work up showed a significantly low platelet count (39,000/microliter) and 6 units were transfused before surgery. The only observations during surgery were ileitis and Meckel's diverticulum. Thrombocytopenia persisted over the first 48 hours after surgery in spite of another transfusion of platelets, with worsening awareness and acute renal failure. After diagnosis of thrombotic thrombocytopenic purpura (TTP), the patient was admitted to the intensive care unit and treatment with fresh plasma and corticoids was started. Two weeks later, after complex evolution and ten sessions of plasmapheresis, the patient was transferred to the hematology ward. TTP must be considered a medical emergency. Platelet transfusions are contraindicated, as they can cause serious clinical deterioration. A low platelet count before surgery should lead to differential diagnosis to determine the cause, with the aim of judging whether platelet transfusion is warranted or not. In some etiological processes, such as in the case we report, platelet transfusion may be life-threatening; corrective measures must be taken early in the process and such transfusion avoided.