All 51 cases of HIV-related malignant lymphoma in Denmark diagnosed from 1983 to 1989 were reviewed. There were 12 Burkitt-type lymphomas, 30 immunoblast-rich lymphomas and 9 other lymphomas. Patients with immunoblast-rich lymphomas had significantly lower CD4 cell counts (median 60 vs. 188 x 10(6)/l, P less than 0.05), and more often a history of previous AIDS-defining illnesses (50% vs. 0%, P less than 0.005), compared with patients with Burkitt-type lymphomas. Epstein-Barr virus (EBV) DNA was demonstrated in 14 of 19 immunoblast-rich tumours, and in 2 of 7 Burkitt-type lymphomas (P = 0.10). Compared with EBV DNA-negative tumours EBV DNA-positive tumours were associated with lower CD4 cell counts (median 39 vs. 188 x 10(6)/l, P = 0.01). It is concluded that two main types of HIV-related malignant lymphoma exist. One is associated with severe immunosuppression, is often of immunoblast-rich morphology, and may be linked to EBV, whereas the other may occur in the absence of immunosuppression, is often of Burkitt-type morphology, and is probably not linked to EBV. In addition to these two main types, other non-Hodgkin lymphomas and Hodgkin's disease do occur.