Intermediate and high-grade non-Hodgkin lymphomas (NHLs) with a B-cell phenotype are acquired immunodeficiency syndrome (AIDS)–defining illnesses. They may increase in frequency as human immunodeficiency virus (HIV)–infected individuals survive longer in an immunosuppressed state with improved antiretroviral treatment and treatment of opportunistic infections. Unusual types of NHL and manifestations of Hodgkin's disease are also seen in HIV-infected individuals. The pathologic and clinical features of the HIV-associated lymphomas, current thinking about their pathogenesis and treatment approaches, and results are the subjects of this article.