Large granular lymphocyte leukemias (LGLL) are chronic clonal lymphoproliferations of mature post-thymic TCRαβ+ CD3+CD4−CD5dimCD8+CD27−CD28− CD45RO−CD57+ T cells (T-LGLL, 85% of cases) or CD3− CD56+ natural killer cells (NK-LGLL) [1–5]. The gene discussed is NCAM1; the disease is T-cell large granular lymphocyte leukemia.