Anemia is common in human immunodeficiency virus infection, particularly in patients with acquired immunodeficiency syndrome. Anemia is multifactorial. HIV infection itself causes anemia, probably as a consequence of HIV infection of stromal cells rather than HIV infection of hematopoietic stem cells. Other common causes of anemia in AIDS are anemia of chronic disease consequent on opportunistic infections, bone marrow suppression by antiretroviral therapy, and hemolytic anemia induced by oxidant drugs. Thrombotic microangiopathy is a significant complication of HIV infection and may respond to plasmapheresis.