Abstract: Diffuse large B-cell lymphoma (DLBCL) is a highly heterogeneous malignant tumor in lymphatic and hematopoietic systems. The majority of the DLBCL patients can be cured with standard chemotherapy, but around 30% to 40% of these patients can suffer from relapse and die from the disease. Double- hit lymphoma (DHL) is an unclassifiable tumor that mainly forms in DLBCL and B- cell lymphoma. The features of this tumor resemble those of DLBCL and Burkitt's lymphoma (BCLU), including short survival time, poor prognosis, and easy relapse. Given these unique characteristics, DHL has attracted much research attention over the years. Although BCLUs are more prone to DHL, DLBCL is the most common lymphoma in DHL. Accordingly, this review focuses on the epidemiology, clinical characteristics, diagnosis, molecular genetics, treatment, and prognosis of double-hit DLBCL.