Individual and multicenter efforts have facilitated the recognition of different parameters with prognostic value at presentation of chronic myeloid leukemia (CML). Interest is currently focused on the prognostic evaluation of features obtained from molecular analysis, and isolation of data with evolutive predictive value. The site of breakpoint within the M-BCR has been suggested as a prognostic factor in some studies. A recent analysis from our group failed to demonstrate differences in either duration of chronic phase or survival between patients with 5' and 3' breakpoints. We have confirmed in a sequential study that a decrease in the expression of some myeloid differentiation antigens of the blood granulocytes can be a prognostic indicator along CML evolution. Our more recent study, separating blast crises on immunological and molecular grounds, confirms lymphoid cases as a distinct subgroup and shows a trend for an association between megakaryoblastic blast crisis and 3' location of the breakpoint.