A 71-year-old man presented with progressively increasing lymphocyte count since the last 12 months. Physical examination was unremarkable. Laboratory studies showed a hemoglobin 13.1 g/dL, leukocytosis of 71.4 K/µL, lymphocyte count of 67.5 K/µL and platelets 172 K/µL. Other tests including whole body PET-CT scan were unremarkable. Peripheral blood smear showed lymphocytosis increased “smudge cells” (A, inset showing smudge cells). Smudge cells were 45% of the total white blood cells. Bone marrow (BM) aspiration and biopsy demonstrated small lymphocytic infiltration with 70% cellularity. Immunohistochemical stains were positive for Cyclin D1 and negative for SOX11. Complex karyotype was detected. FISH studies were positive for IGH/CCND1 and a deletion of TP53. Flow cytometry demonstrated a kappa restricted–monotypic B cell population which was positive for CD5, CD19, CD20, CD22, CD23, CD79b, CD200 (dim), and FMC-7; and negative for CD43 (B). Next generation sequencing based analysis showed TP53 mutation NM_000546.5(TP53):c.389T>A p.L130H. Presence of smudge cells and immunophenotype suggested an initial diagnosis of CLL (chronic lymphocytic leukemia). The smudge cells in this patient were morphologically very similar to typical CLL. Smudge formation in clonal cells is rare in mantle cell lymphoma. Because of the presence of CCND1 gene rearrangement and cyclin D1 positive monoclonal B lymphoma cells in the BM, a diagnosis of leukemic phase of a small cell variant of mantle cell lymphoma was rendered.