Abstract: ODjective : To investigate the characteristics of bone marrow involvement in non-Hodgkin's lymphoma (NHL) by pathomorphology and immunophenotype. Methods : Routine histologic examination was performed on Hematoxylin- eosin(H-E)- stained sections with paraffin emdedded samples of bone marrow biopsies. Phenotype was conducted by immunohistochemistry method. Results : Of 65 Done marrow trephines, 39 were B and 26 were T cell lymphomas. Morphologically the most frequent patterns of NHL bone marrow involvement were mixed and diffused type in B cell lymphomas and interstitial and mixed type in T cell lymphomas. Hairy cell leukemia (HCL) presented a honeycomb appearance, which was special for diagnosis. The morphology of lymphoma cells in the medullary was consistent with extramedullary sites of 26 cases with primary lymphomas. Most lymphomas could be phenotyped by immunohistochemistry. Among 6 cases of small B cell lymphomas unphenotyped, 2 cases should refer to the spleen pathology, 4 cases with bone marrow biopsy alone need to be further phenotyped by other methods. Conclusions : Most of cases with NHL bone marrow involvement show the pathomorphologic and immunophenotypic characteristics definitely, so it could be diagnosed and phe-notyped. Few needs final diagnosis by combination of primary lymphoma and other exams.