Patients with acquired immunodeficiency syndrome (AIDS) are at increased risk of developing non Hodgkin's lymphomas (NHL). Current estimates indicate that 5-10% of HIV-infected individuals develop AIDS-related NHL (AIDS-NHL). AIDS-NHL share several clinical features, including frequent extranodal presentation, aggressive clinical course and poor outcome. However, AIDS-NHL are a heterogeneous group of malignancies. They traditionally included systemic and primary brain lymphomas, but nowadays their updated clinicopathologic spectrum also comprises two novel entities, namely primary effusion lymphoma and plasmablastic lymphoma of the oral cavity. In the last few years, several studies have shown that the pathologic heterogeneity of AIDS-NHL correlates with the heterogeneity of the molecular lesions associated with these lymphomas. However, despite their pathologic and molecular heterogeneity, AIDS-NHL have a common B-cell origin, although the precise stage of B-cell differentiation reflected by the different tumor types has not been clarified yet.