Male patient, 54 years old, post-transplant immune profile, bone marrow transplantation for B-cell Non-Hodgkin's-Lymphoma in 2019 - Peripheral blood sample with white blood count 1,800 cells post-transplant immune profile - marked (42%) Double-Positive proliferation. Panel design, Immunophenotyping and Gating Strategy: Triage of all the samples was analyzed in the LST tube. The TCRCBeta 1 tube was designed based on EuroFlow’s Orientation Tube for Immunodeficiencies (PIDOT), using CD3, CD4, CD8 and CD45 as “backbones”, CD27 and CD45RA to discriminate T-cell subsets, CD16 and CD56 to exclude NK cells, and including TCRCBeta1 in the PE channel. Results: 57% T Cells: *42% Double-positive CD3+ CD7(-) CD27(-) CD45RA+ TCRCBeta1+100% (monoclonal); *7.5% TCD4+ EM CD45RA(-) CD27(-) TCRCBeta1+ 38% (polyclonal); *7.5% TCD8+ EM CD45RA(-) CD27(-) TCRCBeta1+ 38% (polyclonal). Immunophenotype: CD45+ CD3+ CD4+ CD8+ CD26-/+ CD45RA+ CD2+ CD5+ CD11C+ CD57-/+ TCD ALPHA-BETA+ TCRCBETA1+. Negative expression: CD7, CD28, CD45RO, CD25, CD30, TCRGAMA/DELTA, CCR7, CD56, CD16, TCL1. The abnormal Double-positive T-cell population was subsequently detected with a bone marrow sample. The diagnostic conclusion was T-cell Lymphoma, NOS.