The mortality in 15 villages in South-West Uganda was studied in relation to HIV infection. After a population census, serum samples were tested for antibodies to HIV-1. Deaths were ascertained over 2 years. Unequivocal HIV-1 serology results were available for 9389 individuals. The prevalence of infection was 4.8% for all ages and 8.2% for adults (aged 13 or more). 198 deaths were recorded during 15,725 person years of observation. Mortality among seronegative adults was 7.7 per 1000 and among seropositive adults 115.9 per 1000. The excess annual death rate associated with HIV-1 infection was 5.3 per 1000 and in adults 7.9 per 1000. Highest excess mortality was 16.9 per 1000 in the age group 25-34. Among adults, half of all deaths and among those aged 13-44 over 80% of deaths were attributable to HIV-1 infection. These results show the strong impact that HIV-1 infection is having on mortality in a rural area of Uganda where the overall HIV-1 adult prevalence rate is below 10%--a rate lower than in many other parts of East Africa.