Follicular lymphoma (FL) is an indolent lymphoma and may have various clinical courses. FL often involves spleen and bone marrow (BM) but, in contrast to other indolent NHL at diagnosis, very few patients present with an overt detectable leukaemic phase (FLLP). Herein, we present a case report of FL-LP. A 59-year-old female presented with weight loss, increased cervical mass and adynamia initiated few months ago. She brought recent tests with worsening of anemia, lymphocytosis, thrombocytopenia, with normal neutrophil and monocytes counts. A peripheral blood immunophenotyping by flow cytometry showed positive and significant antigenic expression of CD10, CD11c, CD20, CD22, CD23, CD25, CD43, CD79b, CD103, CD123, CD200, FMC7, IgM, IgD and cyKappa, being compatible with Hairy Cell Leukemia. Due the discrepancy between clinical data and flow cytometry findings, probably because of the autofluorescense, the laboratory team asked for a new blood sample that identified characteristics circulating cells of follicular lymphoma with the following immunophenotype: antigenic expression positive and significant of CD10, CD11c, CD20, CD22, CD23, CD43, CD79b, CD200, FMC-7, IgM, IgD and Kappa. Therefore, it was compatible with non-Hodgkin's lymphoma (LNH-B), CD10 positive. PET-CT scan was performed with an intense increase in metabolic activity in cervical, axillary, abdominal lymphonomegalies, in the right pulmonary hilum, as well as along the bone marrow of the axial and appendicular skeleton, with a maximum SUV 19.9. Large splenomegaly associated with a moderate diffuse increase in metabolic activity was also evident. She underwent an excisional biopsy compatible with grade 3A Follicular Lymphoma. This report illustrates an uncommon case of LP-FL and how the correlation between clinic, flow cytometry and morphology is fundamental to correct diagnosis.