Objectives To establish the prevalence of HIV infection in rural South Africa and to investigate demographic factors that influence this prevalence. Design An anonymous HIV seroprevalence survey was performed in conjunction with a population-based malaria surveillance programme. Setting The rural area of northern Natal/KwaZulu, South Africa. Participants A total of 5023 black African participants were recruited by malaria surveillance agents during house-to-house visits; each house in an endemic malaria area is visited approximately once every 6 weeks. Participants included 4044 healthy and 979 febrile individuals (i.e., suspected of having malaria). Main outcome measures HIV-1 and HIV-2 serological status, degree of mobility, age and sex. Results Sixty of the 5023 blood specimens were confirmed to be HIV-1-antibody-positive by Western blot, an overall prevalence of 1.2% (95% confidence interval, 0.9–1.5). None of the specimens was positive for HIV-2 antibodies. After adjusting for age, presence of fever and migrancy, women had a 3.2-fold higher prevalence of HIV-1 infection than men. HIV-1 infection was approximately three times more common among subjects who had changed their place of residence recently (2.9 versus 1.0%, P<0.01). Conclusions The prevalence of HIV-1 infection is higher among women than men resident in rural Natal/KwaZulu, South Africa. This is at least in part the result of oscillatory migration, particularly of men who work in urban areas but have families and homes in rural areas. Migration is associated with a higher prevalence of HIV-1 infection, suggesting that improving social conditions so that families are not separated and become settled in their communities is one way to help reduce the spread of HIV-1.