A 54-yr-old female having chronic neutrophilic leukemia (CNL) associated with severe liver injury is presented. Physical examination on admission showed severe jaundice, hepatosplenomegaly, massive ascites, and pretibial edema. Complete blood count showed a hemoglobin level of 9.1 g/dL, platelet count of 25.8 x 10(4)/microL, and white blood cell count of 36.6 x 10(3)/microL with 89.7% neutrophils. Blood chemistry showed hyperbilirubinemia (21.9 mg/dL) with normal transaminase levels. There was no abnormality in serum cholesterol, triglyceride, or glucose levels. Neutrophil alkaline phosphatase activity was significantly elevated. Bone marrow aspiration showed myeloid hyperplasia with normal karyotype. Rearrangement of the bcr/abl was not detected by either polymerase chain reaction or fluorescence in situ hybridization. Human androgen receptor gene assay (HUMARA) of the bone marrow cells showed clonal proliferation of neutrophils. The patient was diagnosed as having CNL. To evaluate the pathogenesis of the liver injury, a needle biopsy was performed, which showed steatohepatitis with infiltration of neutrophils. As the patient had no history of alcohol abuse, a diagnosis of non-alcoholic steatohepatitis (NASH) was made. Assuming that the infiltration of abnormal neutrophils into the liver contributed to the development of NASH, she was treated with cytoreductive chemotherapy (cytosine arabinoside: 100 mg/d, 1-3 doses/wk). With decreases in white blood cell counts, serum bilirubin levels decreased gradually to 1.5 mg/mL. A postchemotherapy liver biopsy specimen showed marked improvement of the fatty degenerative change. To our knowledge, this is the first report describing the development of NASH in a myeloproliferative disorder. We believe that the infiltration of leukemic cells contributed to the development of NASH in this patient.