A 5-year-old girl developed acute lymphoblastic leukemia (T-ALL) 15 months after being diagnosed with autoimmune hemolytic anemia (AHA), while AHA was in partial remission. AHA was mediated by warm antibodies. Because AHA could not be controlled during the induction therapy of ALL, she was administered immunoglobulin G and plasmapheresis was performed. Hepatomegaly dissappeared in the 4th month. However, anemia requiring blood transfusion, positive direct Coombs' test, and splenomegaly dissappeared in the 13th month of the leukemia treatment; reticulocytosis and decreased haptoglobin level persisted. AHA exacerbated in the 24th month of the ALL therapy. Prednisolone was started but the family refused to continue the therapy. This case presents some features that were not reported before, such that ALL was preceded by AHA and involved T-cell lineage, AHA was mediated by warm antibodies, and the two disorders took place in childhood.