The lack of distinguishing characteristics between lymphoid blastic crisis (BC) of Philadelphia (Ph)+ chronic myeloid leukemia (CML) and Ph+ acute lymphoblastic leukemia (ALL) remains an exciting dilemma. Indeed, the genetic defect of approximately half of Ph+ ALL patients is identical to that identified in CML. Here we report the case of one patient admitted with immunological and molecular patterns indicative of Ph+ ALL. The patient was brought into complete remission by chemotherapy and was transplanted with an HLA identical sibling donor, but relapsed a few months later with immunological and molecular evidence of BC of CML, displaying myeloid markers and lacking lymphoid antigens and immunoglobulin heavy chain (IgH) rearrangement. This suggest a CML case with an initial BC without a previous chronic phase or supervening on a subclinical CML.