Abstract : The Rakai Project conducted a population-based cohort study in rural Rakai District, Uganda, a region with high rates of HIV prevalence. The cohort population described here was followed between 1990 and 1992 and consisted of all residents aged 15 years or more living in 1945 households in 31 community clusters. A detailed census was conducted at baseline in every study household. Census data were updated annually, and all inter-survey deaths, births, and migrations were recorded. Immediately following each annual census, all consenting adults were administered a socio-demographic, behavioural and health survey, and provided a blood sample for HIV testing. HIV prevalence in the study population was high, with 19.1 per cent of adults aged 15 or more years being HIV-positive. By household, the burden of infection was even more pronounced: 31.3 per cent of households had at least one HIV-infected resident adult. Twenty seven per cent of heads of households were also HIV-positive. Overall, 3.6 per cent of study households experienced the death of an HIV-positive adult per year, and another two per cent lost an HIV-negative adult. HIV-related adult mortality had substantially more effect on subsequent household dependency ratio and on material possessions than the death of an HIV-uninfected adult, in part because the former deaths were concentrated in adults aged 15-49, the most economically active age group in this rural population. Just under 15 per cent of children aged 14 years or less had lost one or both parents, and approximately half of these parental losses are estimated to be associated with HIV infection. Nineteen per cent of study households reported at least one resident child who had lost one or both parents. Although there is evidence that loss of a parent is associated with lower school attendance, orphans overall continue to be absorbed by community households which are headed by adults. HIV infection is very prevalent among adults in Rakai and the associated mortality imposes a substantial social and economic burden on households in the district.