The cryptic translocation t(12;21)(p13;q22), which leads to the TEL-AML1 fusion gene, is the most common abnormality in childhood B-cell ALL.     ///    A fluorescence in situ hybridization study of TEL-AML1 fusion gene in B-cell acute lymphoblastic leukemia (1984-2001)..     ///    No TEL-AML1 fusion was observed in the 26 ALL adults.     ///    "Our results (frequency of TEL-AML1 fusion in children and of the deletion of the untranslocated TEL allele, mean age of the patients and white blood cell count) are within the range observed by others. "    ///    A deletion of the untranslocated TEL was observed in 36.3% of the ALL with the TEL-AML1 fusion.     ///    The aim of this retrospective study was to determine the incidence of TEL-AML1 fusion in childhood and adult B-cell ALL using interphase fluorescence in situ hybridization (I-FISH) and its association with additional changes.     ///    The coexpression of myelocytic and B-lymphoid antigens was found in 3 of the 11 of TEL-AML1 fusion positive-ALL. 