A 71-year-old man under observation for peptic ulcer in OPC developed fever and complained of back pain on the left side. Physical examination revealed splenomegaly and subcostal tenderness on the left side, and the peripheral blood test showed elevated WBC and an inflammatory reaction. The patient was admitted to the hospital for further tests on the same day. Abdominal ultrasonography showed distinctive splenomegaly and a scattering of definitely hypoechoic regions, triangular in shape, centered on the splenic capsule; indefinite hypoechoic lesions of varying sizes also appeared. Splenomegaly resulting from myeloproliferative disorders accompanied by splenic infarct and abscess was suspected. Splenectomy was performed because the back pain increased in intensity and rupture of the spleen was anticipated. The extirpated spleen measured 23×15×5 cm and weighed 1,400 g. No abscess was observed in the spleen, but infarcts and notably congested areas were present. Preoperative echograms matched the gross pathologic findings. Microscopic findings included bleeding accompanying exogenous hematopoiesis and infarct, and a diagnosis of myelofibrosis was made. Post-operative chemotherapy had been considered, although the patient died as a result of multiple organ failure and recurrence of hemorrhagic peptic ulcer 21 days after surgery. This study is based on this very rare case of hemorrhagic splenic infarction accompanying myelofibrosis, and the ultrasonic findings are attached.