HIV-infected individuals have a high risk of developing non-Hodgkin lymphoma (NHL). In Europe, the prevalence of AIDS with a concurrent NHL diagnosis increased from 3.6% to 5.4% between 1994 and 2000. In population-based record linkages between cancer registries and AIDS registries in the USA, Italy, and Australia, the relative risks of NHL in people with AIDS ranged between 15 for low-grade and T-cell NHL and 400 for high-grade NHL. The corresponding relative risk of Hodgkin's disease was about 10, whereas the risks for multiple myeloma and leukaemias were in the range 2 to 5. Since the introduction of highly active antiretroviral therapy in the more developed countries (1996), most studies have suggested a decline in the incidence of some types of NHL, most notably the primary brain form. In studies from Africa, the risk of HIV-associated NHL is about ten times less than that in the more developed countries, but underascertainment and earlier death from other AIDS-related illnesses may explain the relative lack of HIV-associated lymphomas.