Chronic neutrophilic leukemia(CNL) is a very rare myeloproliferative disease, characterized by sustained mature neutrophilic leukocytosis with granulocytic bone marrow infiltration, high NAP(neutrophilic alkaline phosphatase) score and absence of philadelphia chromosome, It is frequently accompanied by hepatosplenomegaly, elevated serum vitamin B_12 and uric acid level. For the diagnosis of CNL, the leukemoid reaction, especially secondary to neoplasia, infection and autoimmune diseases, should be excluded.

Since Tuohy's first description in 1920, more than 50 cases fullfilling the above criteria have been reported worldwide, and 4 cases in Korea. Several authors have demonstrated the defect of intracellualr killing in the mature neutrophil and this finding correlates well with the very high incidence of fatal infection, The hemorrhagic diasthesis in CNL is caused by functional abnormality of the platelet. This disease has tendency to transform to blastic crisis and acute leukemia as in other myeloproliferative disease, but characteristically shows frequent coexistence with multiple myeloma. Until now , the therapeutic trials in CNL have been disappointing. Hydroxyrea and busulfan can control hyperleukocytosis. On the basis of functional defect in neutrophil, alpha-2b-interferon has been tried and several reports have demonstrated the clinical and functional effect of interferon on CNL.

CNL is very rate hematologic disease and there are few report about general aspect of disorder. We report here a typical CNL case presenting with splenomegaly and leukocytosis with a review of the literature.