A 59-year-old female diagnosed with JAK2 617-positive polycythemia vera (PV) and treated with phlebotomies for 13 years developed progressive splenomegaly and decreased needs for phlebotomy. Myelofibrosis was considered, but not confirmed by bone marrow examination. Laboratories tests showed hemoglobin, 92 g/L; platelet count, 119 × 109/L; white blood cell count, 8.6 × 109/L; and lymphocytes, 1.71 × 109/L.,with medium-sized lymphoid cells with indented nucleus, blue cytoplasm, and circumferential projections on smear (panel A solid arrow). BM showed hypercellularity, increased number of abnormally lobated megakaryocytes (panel B solid arrows), and diffuse infiltrates of lymphoid cells (panel B dotted arrows). Flow cytometry showed a ? light chain–restricted clonal B-cell population positive for CD19/20/FMC7/103 and bright CD11c, but negative for CD5/23/10/25/103; molecular analysis was negative for BRAF V600E mutation, findings consistent with hairy cell leukemia variant.