B-cell lymphoma, unclassifiable, with features intermediate between diffuse large B-cell lymphoma (DLBCL) and Burkitt lymphoma (BL), is a new category in the 2008 World Health Organization’s classification of hematologic neoplasms, which includes cases that have features of both diseases but which cannot be classified easily into either. These lymphomas generally have a poor outcome. This classification is not intended to represent 1 disease but rather a spectrum of lymphomas with overlapping features. Such cases may include those with characteristic BL cytology but with an atypical immunophenotype (strongly BCL2 positive, Ki-67 < 90%) or those with an immunophenotype compatible with BL but with a greater degree of morphologic heterogeneity and genetic complexity. Identification of these lymphomas requires the integration of multiple data points including morphology, immunophenotype, and genetic features. They are important to recognize because they do not typically respond well to standard therapies for either BL or DLBCL, and clinical trials are necessary to determine the optimal treatment of these aggressive lymphomas.