In this study, we analyzed the expression levels of multiple T-cell-associated markers (CD2, surface (s) and intracellular (i) CD3, CD4, CD5, CD7, and CD8) and others (CD10, CD34, CD45, CD48, CD99, and HLA-DR) in the bone marrow (BM) at diagnosis and during follow-up in pediatric patients with T-ALL. This evidence concerns the gene CD99 and acute lymphoblastic leukemia.