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A 73-year-old female presented with weakness, weight loss, back pain, and marked lymphocytosis  (WBC 114 x 109/L; 98% of white blood cells). Imaging showed a large mediastinal mass and left hilar lymphadenopathy. Peripheral blood flow cytometry showed the abnormal cells are positive for CD19, CD20, CD45, and kappa; negative for CD5, CD10, CD23, CD25, CD103, CD11C, TdT, IgM, CD33, CD34, CD117, and lambda. (a-b) Bone marrow aspirate and biopsy showed diffuse infiltration consisting of 2 admixed populations of atypical cells: (1) large cells with nuclear molding, high N/C ratio, and inconspicuous nucleoli (black arrows); (2) small lymphoid cells with scant cytoplasm and condensed chromatin (green arrows). The large cells are positive for CAM5.2 (c), AE1/AE3, CD56, synaptophysin (weak), TTF-1, and express high Ki-67 (60-80%). The small cells are positive for CD20 (d), CD79a, PAX5, and are kappa light chain-restricted (d: inset). These findings are consistent with metastatic small cell carcinoma and B-cell lymphoma involving the bone marrow simultaneously. We present this case to highlight the rare coexistence of hematologic malignancy and metastatic solid tumor in the bone marrow. Thorough morphologic and immunohistochemical evaluations are crucial to avoid misdiagnosis.