Like other immunodeficient populations, HIV-infected individuals are at risk for developing high grade B-cell malignancies. The aetiology of these lymphomas remains unknown. While the tumours share many of the features of B-cell lymphomas seen in immunosuppressed transplant recipients, unlike transplant recipients, Epstein-Barr virus genomic sequences are identified in only a small minority of peripheral lymphomas from HIV-infected individuals. The majority of lymphomas are classified as diffuse, large-cell tumours of either the intermediate grade type or the high grade immunoblastic type. However, approximately one-third of patients present with high grade, small, non-cleaved cell lymphomas. Patients typically present with widespread extranodal disease, often at unusual sites. Lymphoma confined to the central nervous system has been observed in approximately 25% of HIV-infected patients with non-Hodgkin's lymphoma. The therapeutic outcome and survival in these patients has been disappointing. Complete response is achieved less frequently, relapse rates are higher and survival generally shorter than those observed in non-HIV-infected patients with non-Hodgkin's lymphoma. Prognosis is better for those patients without a prior AIDS diagnosis, who have higher total CD4 cell counts, good performance score, absence of an extranodal site of disease, and treatment with more moderate doses of chemotherapy. Hodgkin's disease, while not causally linked to the presence of immunodeficiency, appears to have a more aggressive natural history in the patient with HIV infection. Advanced disease at presentation is the rule, and the response to therapy has been poor with associated short survivals. Poor bone marrow reserve and the occurrence of intercurrent opportunistic infections has made it difficult to administer many of the standard chemotherapeutic regimens now used for the treatment of Hodgkin's disease.