Thrombotic microangiopathy (TMA) after hematopoietic stem-cell transplantation (HSCT) or solid-organ transplantation is a serious complication that may be associated with diverse clinical conditions. The reported incidence varies widely, in part due to different diagnostic criteria. Currently, the diagnosis is based mostly on clinical features and is often uncertain; many disease or therapy-related complications in transplantation and malignancy can manifest clinical features of TMA. Risk factors for TMA post HSCT include the type of conditioning regimen, the presence graft-versus-host disease (GVHD), the use of calcineurin inhibitors (cyclosporine and tacrolimus) for GVHD prophylaxis, and infection. Cyclosporin and tacrolimus are the most commonly reported agents associated with TMA in solid-organ (mainly kidney) transplantations. Cancer-related TMA may be associated with chemotherapy or the malignancy itself. Compared with idiopathic TMA (thrombotic thrombocytopenic purpura), the outcome for patients with TMA post-HSCT or disseminated malignancy is poor. The efficacy of plasma exchange in the treatment of TMA post-HSCT or malignancy is uncertain. In the future, objective criteria integrating laboratory features (including tissue pathology, quantitative hematology, and endothelial cell functionality) with clinical features may assist in the diagnostic accuracy of TMA post HSCT, which would allow better evaluation of treatment modalities and better prediction of prognosis and outcomes.