To assess the likely impact on HIV incidence of increased condom use, a reduction in casual sexual partners, treatment programmes for other sexually transmitted diseases (STD) and combinations of these in rural Uganda. A simulation model for the transmission dynamics of HIV infection and STD was employed, drawing on data from a rural population cohort in South-West Uganda with an HIV prevalence of 9% among adults in 1990. For the scenario most consistent with data from the study population, 39% of all adult HIV infections were averted, in the 10 years from 1990, when condoms were used consistently and effectively by 50% of men in their contacts with one-off sexual partners (such as bar girls and commercial sex workers). Reducing by 50% the frequency of men's sexual contacts with one-off partners averted 68% of infections. Reducing by 50% the duration of all STD episodes averted 43% of infections. Combining these three interventions averted 82% of all adult infections in the 10 years from 1990. A substantial proportion of HIV infections may be averted in general populations through interventions targeted only on less regular sexual partnerships.