Among 235 patients with CML we reviewed 91 patients with BC diagnosed between 1980 and 1995; 15 of the 91 (16%) developed extramedullary disease (EMD). The sites involved were the lymph nodes (13/15), CNS (1/15) and suborbital mass (1/15). The appearance of EMD was associated with chronic phase (CP) features in the bone marrow in 3/15 cases, with accelerated phase (AP) in 3/15 and with BC in 9/15. 11/15 (73%) cases of EMD were classified as myeloid (My-EMD) and 4/15 as lymphoid-type (Ly-EMD): three B-phenotype and one T-phenotype. All Ly-EMD cases were treated with vincristine, daunorubicin and prednisone and obtained complete remission (CR). Cases of My-EMD were treated with daunorubicin and cytosine arabinoside, of which only 1/11 achieved CR. We suggest that in EMD also, the type, lymphoid or myeloid, of BC has a bearing on treatment response and prognosis: Ly-EMD is more responsive to treatment and has longer survival than My-EMD.