T-cell large granular lymphocytic leukemia (T-LGLL) is a rare chronic lymphoproliferative disorder of mature cytotoxic T-cells. Accurate diagnosis relies on the integration of morphologic, immunophenotypic, molecular, and clinicopathologic findings. This study examined the frequency of abnormal findings in cases with clinical or hematopathologic suspicion for T-LGLL to investigate the relative importance of each diagnostic entity. This is a retrospective review of cases with clinical or hematopathologic suspicion for T-LGLL with concurrent flow cytometry, next-generation sequencing of STAT3/STAT5B, and T-cell receptor gene rearrangement (TCR) at a single academic institution from 2017-2019. Clinicopathologic information was abstracted from the chart.