Background: Apoptosis and cell cycle regulation play an important role in pathogenesis and tumor progression in patients with Diffuse Large B-Cell Lymphoma (DLBCL). Bcl-2 associated athanogene-1 (BAG-1) is an antiapoptotic protein as well as a regulator of cell growth. There is no conclusive evidence about BAG-1 protein expression in this disease. Objective: To investigate the expression level of BAG-1 protein in DLBCL. Methods: Thirty patients diagnosed from 1997-2004, as having DLBCL, were selected. Also 30 normal lymph nodes were included as normal counterparts in this study. BAG-1 expression was determined by immunohistochemical staining in both DLBCL and normal lymph node samples. Results: Of the 30 DLBCLs examined, 100% were positive for nuclear and 83% were positive for cytoplasmic BAG-1 staining. Of the 30 normal lymph nodes investigated, 20% were positive for nuclear and 0% were positive for cytoplasmic BAG-1 staining. Nuclear staining in DLBCL samples was significantly higher than those of normal lymph nodes (100% versus 20%, p <0.001). Besides, cytoplasmic staining in DLBCL samples was significantly higher than those of normal lymph nodes (83% versus 0%, p <0.001). There was no association between BAG-1 staining and patients' overall survival. Conclusion: Our data indicated that BAG-1 protein was deregulated in this disease similar to some other malignancies such as breast and colon cancer. Overexpression of BAG-1 in DLBCL suggests that this protein probably plays an important role in the pathogenesis of DLBCL. Besides, higher nuclear BAG-1 staining might be correlated with poor prognosis.