BACKGROUND Chemotherapy intensification may lead to new forms of toxicity such as hemolytic uremic syndrome. METHODS Three patients are described who developed this complication 4 to 6 months after high dose chemotherapy followed by autologous stem cell support. The literature on this subject is reviewed. RESULTS One patient was conditioned with BEAC (carmustine, etoposide, cytosine arabinoside, and cyclophosphamide) and received autologous bone marrow. The other two underwent triple peripheral stem cell transplantation after conditioning with CTC (carboplatin, cyclophosphamide, and thiotepa). Symptoms were hypertension, microangiopathic hemolytic anemia, thrombocytopenia, and renal insufficiency. One patient had a retinal vein thrombosis. One patient died of a cardiac arrest shortly after the diagnosis was made. The remaining two achieved a partial remission: one with fresh frozen plasma without plasmapheresis and fresh frozen plasma, but improved on high dose intravenous immunoglobulin and vincristine. CONCLUSIONS Hemolytic uremic syndrome is a serious complication of the more intensive chemotherapy made possible by stem cell support. Because of the rapidly growing indications for this approach, an increase in this type of vascular complication is expected.