Bleeding is a common complication of such myeloproliferative disorders as polycythemia vera, and it usually occurs in either the skin or mucosa. We experienced a case of a massive retroperitoneal hematoma with no history of trauma in association with polycythemia vera. A 68-year-old man was referred to our hospital as a case of acute abdomen, and was diagnosed as having a retroperitoneal hematoma and polycythemia vera based on radiological and hematological examinations. Because the mass effect of the hematoma caused a progressive deterioration of his respiratory condition, surgical drainage was necessitated and successfully undertaken. Although conservative treatment is reportedly sufficient and uncontrollable intraoperative bleeding may occur, especially in cases of myeloproliferative disorders, our experience suggests that an operation may nevertheless be occasionally advisable for this rare condition.