A 37-year-old man was admitted because of pancytopenia with leukoerythroblastosis and anisocytosis in January 1986. Bone marrow aspiration resulted in a dry tap and biopsy showed marked myelofibrosis. Three months after admission, generalized lymph node swelling and multiple skin tumors were recognized. A biopsied lymph node revealed lymphoblastic lymphoma. The surface markers of lymphoma cells showed an immature T-cell phenotype, whereas T-cell receptor beta and gamma chain genes showed germ line configuration. The patient was treated with combination chemotherapy in June 1986. A month later, he developed leukemic transformation with features of acute myelocytic leukemia and he died of pneumonia. Autopsy disclosed extramedullary hematopoiesis in the liver and spleen. Primary myelofibrosis complicated by T-cell lymphoma is extremely rare.