We report a case of thrombotic thrombocytopenic purpura (TTP) in a 47-year-old woman, who presented fluctuating visual disturbances which had developed over the last six months. An antiphospholipid syndrome was suspected and intravenous heparin treatment was started. One week later, hemolytic anemia and renal insufficiency occurred. Severe deficiency of von Willebrand factor-cleaving protease was found and a diagnostic of TTP was made. The clinical outcome was favorable after treatment with plasmapheresis and fresh frozen plasma. Diagnosis, etiology and treatment of this life-threatening disease are discussed.