A 55-year-old female with a history of psychosis and rheumatoid arthritis was admitted to the hospital for fatigue and dizziness. At admission, macrocytic anemia, high serum lactic acid dehydrogenase (LDH) and gastrin concentrations, decreased serum vitamin B12 concentration, with macroovalocytes and poikilocytes in peripheral blood smear suggested the diagnosis of pernicious anemia. Indirect antiglobulin test (IAT) was negative. Surprisingly, treatment by vitamin B12 and folic acid administered for two weeks was ineffective and followed by transitory worsening of hemoglobin concentration on day 8. Repeat direct antiglobulin test (DAT) and IAT were positive. This immunotransfusion conversion, suggesting the presence of autoimmune hemolytic anemia, could be explained by change in the macroblastic erythrocyte population, i.e. emerging red cells with completely exposed membrane antigens due to vitamin B12 treatment and/or higher degree of dysregulation of the lymphocyte clone secreting erythrocyte autoantibodies. We proposed the coexistence of pernicious and autoimmune hemolytic anemia; therefore, methylprednisolone was added to vitamin B12 treatment. This therapy successfully improved hemoglobin and erythrocyte concentration. Although megaloblastic-pernicious anemia is a common disease, association of pernicious and autoimmune hemolytic anemia with two mechanisms of hemolysis (ineffective erythropoiesis and immune mechanism) is a rare condition, with only several dozens of cases described so far.