An autopsy case of a 42 year old man with the anerythremic form of acute erythremic myelosis (Di Guglielmo's syndrome) is reported. The patient was admitted because of a 1 month history of fatigue and fever. Physical examination showed hepatosplenomegaly. Laboratory data showed leukopenia, mild normocytic anemia, and high levels of serum lactate dehydrogenase and vitamin B12. Bone marrow aspirate revealed an elevated number of erythroblasts, with dyserythropoiesis (E/M = 3.7). After admission, thrombocytopenia progressed rapidly, but blast cells were not seen in the peripheral blood throughout the clinical course. On the 56th hospital day, the patient died of pneumonia. At autopsy, the spleen weighed 550 g and the liver 1800 g. Histologically, the white and red pulps of the spleen and the portal region and sinusoid of the liver were diffusely infiltrated by blast cells that were positive for anti-hemoglobin (Hb) antibody on immunoperoxidase staining. The bone marrow, the lymph nodes, the adrenal glands, the pancreas, and the heart were also infiltrated by the blast cells. This was thus considered to be a rare case of the anerythremic form of acute erythremic myelosis (Di Guglielmo's syndrome), the findings showing that Hb immunoperoxidase staining is useful for the diagnosis of this condition.