A syndrome of microangiopathic hemolytic anemia, renal dysfunction and neurological abnormalities was first noted in bone marrow transplant recipients 22 years ago. Now known as transplantation-associated thrombotic microangiopathy (TA-TMA) to distinguish it from other thrombotic microangiopathies, this disorder responds poorly to conventional treatments for thrombotic thrombocytopenic purpura. In this review, we discuss the incidence and risk factors for TA-TMA and describe a pathophysiologic model of the disorder based on results obtained from laboratory models of the thrombotic microangiopathies. We conclude by suggesting possible approaches to the early diagnosis and treatment of TA-TMA based on this model that may warrant testing in future clinical trials.