Warm autoimmune hemolytic anemia (WAHA) leads to accelerated red-cell destruction due to the presence of warm agglutinins (almost always IgG antibodies) that bind to antigens on erythrocytes at a temperature of 37°C. The annual incidence of WAHA is 1 to 3 cases per 100,000 persons. The median age of onset is 52 years, but WAHA may occur at any age, and there is a slight female predominance in most series. Up to 30% of patients have a durable remission after initial therapy, but the rest have a chronic, relapsing course.