The incidence and characteristics of HIV-associated lymphoma among a cohort of patients infected predominantly through intravenous drug use are reported. Fifty-one definite cases were identified, occurring in a total cohort of approximately 1,340 individuals. The rate at which lymphoma occurred as the AIDS-defining illness did not differ significantly from that in previously published studies in which there was a preponderance of men infected through homosexual intercourse, and it was strikingly similar for all patient groups within this cohort. In patients diagnosed before death, the median survival was 103 days. Patients presenting with cerebral lymphoma had more advanced HIV infection and a shorter survival (median of 49 days compared with 149 days for extracerebral lymphoma). Although there is an apparent excess of cases (expressed as cases per 1,000 years of follow-up) among homosexual men, this is likely to be due to confounding factors, and these sources of possible bias are discussed. These data do not support the hypothesis that rates differ between different patient groups.