Translocation of the LYL1 oncogene are rare in T-cell acute lymphoblastic leukemia, whereas the homologous TAL1 gene is rearranged in approximately 20% of patients. Previous gene-expression studies have identified an immature T-cell acute lymphoblastic leukemia subgroup with high LYL1 expression in the absence of chromosomal aberrations. Molecular characterization of a t(7;19)(q34;p13) in a pediatric T-cell acute lymphoblastic leukemia patient led to the identification of a translocation between the TRB@ and LYL1 loci. Similar to incidental T-cell acute lymphoblastic leukemia cases with synergistic, double translocations affecting TAL1/2 and LMO1/2 oncogenes, this LYL1-translocated patient also had an LMO2 rearrangement pointing to oncogenic cooperation between LYL1 and LMO2. In hierarchical cluster analyses based on gene-expression data, this sample consistently clustered along with cases having TAL1 or LMO2 rearrangements. Therefore, LYL1-rearranged cases are not necessarily associated with immature T-cell development, despite high LYL1 levels, but elicit a TALLMO expression signature.