CBFB and myeloproliferative disorder: Harlequin cells-abnormal eosinophils containing basophilic granules-are well described in acute myeloid leukemia (AML) with <i>CBFB::MYH11</i> fusion, but their diagnostic relevance in CML has not been systematically assessed.<h4>Methods</h4>We retrospectively reviewed 177 peripheral blood smears: 53 CML; 30 non-CML MPN and related disorders; 59 AML (including three with <i>CBFB::MYH11</i> fusion); 11 eosinophilia; and 24 reactive cytosis cases.