Non-bacterial thrombotic endocarditis (NBTE) was frequently identified in early post-mortem studies of patients with HIV infection, but has not been reported since 1989. The reason for this apparent decline is not clear, but it is possible that the prevalence of the condition was overestimated in the past. We have found no evidence of NBTE in our series of 110 autopsies on subjects from all major risk groups and at various stages of immune deficiency [intravenous drug user (IVDU)-AIDS 35% (39/110), IVDU-pre AIDS 36% (40/110), homosexual-AIDS 25% (28/110), blood product recipients-AIDS 1.8% 2/110), African 0.9% (1/110)]. Infective endocarditis (IE) in HIV infection occurs almost exclusively in intravenous drug users and is rare in other HIV-positive patients. However, asymptomatic HIV infection appears to have little effect on the susceptibility to or the mortality from endocarditis and it is, therefore, appropriate to institute antimicrobial treatment in these cases. The majority (54.4%) of the 960 HIV-positive individuals in the Lothian region of Scotland are young adults who contracted the virus through IVDU around 1983. However, a prospective echocardiological study of 269 patients over four years (IVDU 69%, homosexual 18%, heterosexual 8%, bisexual 3%, multiple risk factors 1%) has demonstrated only four cases of infective endocarditis. We believe this reflects the prevalence of current parenteral drug use in our cohort which has fallen with the introduction of an oral drug replacement programme.(ABSTRACT TRUNCATED AT 250 WORDS)