Certain neoplasia are closely associated with acquired immune deficiency syndrome (AIDS). To evaluate this relationship the authors reviewed the occurrence of lymphomas in populations at high risk for AIDS; the study population included prisoners from New York State and nonprisoner intravenous drug abusers (IVDA). Non-Hodgkin's lymphoma was diagnosed in 16 prisoners, all of whom were IVDA, and four nonprisoner IVDA. The observed number of prisoners with non-Hodgkin's lymphoma (11) diagnosed between January 1, 1981 and December 12, 1984, significantly greater than the expected number (2.28) based on age adjusted incidence rates for the US population (P less than 0.001). The calculated average incidence rate for non-Hodgkin's lymphoma among New York State prisoners aged 20 to 49 years was 21.5/10(5) to 67.2/10(5), which was nearly sixfold to 18-fold higher than the general population. For prisoner IVDA, specifically, this incidence may be as high as 164/10(5), which represents a 40-fold increase in the relative risk compared with the general population. It is concluded that, non-Hodgkin's lymphoma is frequently a manifestation of AIDS among IVDA, and is the most common malignancy seen in IVDA with AIDS.