A case of chronic neutrophilic leukemia (CNL), a rare myeloproliferative syndrome associated with monoclonal gammopathy of uncertain significance (MGUS-Type IgGk), is reported. Karyotypic study, carried out on bone marrow, excluded Philadelphia-pos. chronic myeloid leukemia (CML) and showed Y loss (45 XO). Only a few cases of CNL with paraproteinemia have been reported, but no case of associated karyotypic abnormalities and paraproteinemia has so far been described.