In this case report, we describe for the first time a patient with thrombotic thrombocytopaenic purpura (TTP) accompanying highly active systemic lupus erythematosus (SLE) that was associated with non-neutralizing antibodies against the plasma metalloprotease ADAMTS13. Those non-neutralizing antibodies could have been the cause of ADAMTS13 depletion and consecutive TTP. More extensive analyses are required to determine the prevalence as well as the clinical relevance of non-neutralizing antibodies against ADAMTS13 in SLE patients.