We herein report a rare case of Ph chromosome-negative acute T-lymphoblastic leukemia (T-ALL) with a classical BCR rearrangement seen in chronic myelogenous leukemia (CML). There were no clinical or morphologic features to suggest a previous chronic phase of CML. The importance of a full analysis of the BCR gene in the case of adult acute lymphoblastic leukemia (ALL), especially in T-ALL, are discussed.