Autoimmune hemolytic anemia (AIHA) is a relatively uncommon disorder caused by the increased destruction of red blood cells (RBCs) by anti-RBC autoantibodies with or without complement activation. AIHAs can be distinguished on the basis of the autoantibody Ig class and thermal characteristics, i.e. the optimal temperature of reaction with autologous erythrocytes, in warm (wAIHA), cold (cold agglutinin disease; CAD), and mixed forms, although atypical cases of difficult diagnostic classification are reported with increasing frequency. Moreover, AIHAs are classified in primary (idiopathic), in which hemolysis dominates the clinical picture in the absence of any other coexisting disorder, and in secondary forms, accompanying and complicating an underlying disease. AIHA may develop gradually, or have a fulminant onset with life-threatening anemia. The diagnosis is usually simple, based on the presence of hemolytic anemia and serological evidence of anti-erythrocyte antibodies, detectable by the direct antiglobulin test (DAT).