Lymphomas are tumors of the lymphatic system, but its cells, mainly lymphocytes constitute morphological substrate of the immune system. Lymphocytes are characterized by the expression of several antigens manifested in subsequent stages of development. These, so called differentiation antigens grouped in CD classification are also expressed in lymphomas. They may be traced by means of various methods, and in particular, by flow cytometry. The latter has not only diagnostic function, but also permits to detect residual disease and allows for monitoring of neoplastic process in the course of anti- tumor therapy. Diagnostics of lymphomas is still based on histopathological assessment of tissue sections. Flow cytometry constitutes however valuable complement, providing quantitative data of positive cells, percent of proliferating ones, DNA ploidy, and above all, fast response. It does not however, provide information about topography of lesion. Cells for flow cytometry may originate not only from blood or bone marrow, but also from oligobiopsy of tumor or lymph node. Marked and steadily growing number of known differentiation antigens creates vast possibilities for the evaluation of not only B-cell but also T-cell and NK-cell tumors. Technology of flow cytometry, based on the assessment of several thousands of living cells in the laser beam, subjected previously to the reaction with fluorochrome labelled monoclonal antibodies – is relatively simple and permits to obtain comprehensive results within couple of hours. In summary, the data presented, with the examples of cytometric diagrams, show unequivocally, that parallel use of flow cytometry with morphological assessment of tissue section may constitute „gold standard” in diagnostics and monitoring of this group of malignancies.