Thrombotic thrombocytopenic purpura (TTP), which is typically characterized by fever and central nervous system manifestations and hemolytic uremic syndrome (HUS), in which renal failure is a prominent feature are the most common thrombotic microangiopathies (TMAs). TTP is usually associated with a severe deficiency of ADAMTS13 [a metalloproteinase involved in the degradation of von Willebrand factor (vWF) multimers], causing excessive accumulation of ultra-large vWF multimers and platelet aggregation with organ failure. By contrast, patients with HUS or other TMAs usually display a normal or at least detectable ADAMTS13 activity. A TMA may be occasionally developed in association with HELLP (haemolysis, elevated liver enzymes, and low platelet count) syndrome, infections, cancer and bone marrow transplantation. In cancer patients, TMA may be related to chemotherapeutic regimens or the malignant disease itself. Occasionally, TMA is the first manifestation of an occult cancer, and in large series approximately 3% of patients who were originally diagnosed with TTP, were in fact harboring an occult malignancy. The pathogenesis of cancer-associated TMAs is not completely elucidated, but probably the most important factor is endothelial damage. However, cancer-associated TMAs show some distinct features that should promptly lead to complementary investigations for an underlying malignancy. Weakness, cough and dyspnoea, fever, weight loss, bone and abdominal pain are the most common presenting symptoms. Generally, biochemistry reveals markedly increased LDH levels, increased alkaline phosphatase and the blood smear shows erythromyelemia. Bone marrow biopsy is a valuable tool in order to establishing malignant seeding. Treatment of the underlying neoplasia is the mainstay of therapy and there is no role for plasmapheresis or plasma infusions.