Southern Africa has among the highest rates of HIV-1 infection in the world as judged by cross-sectional HIV-1 prevalence surveys carried out among women attending antenatal clinics. Incidence rates, which provide information on the number of new cases of infection, are more informative of the current state of the epidemic than estimates of prevalence, which provide information on the rates averaged over some previous time. Cohort studies to measure incidence rates are expensive and difficult to carry out, however, and few have been done in Africa. A recently developed standardized algorithm for recent HIV-1 seroconversion (STARHS) based on a sensitive/less-sensitive enzyme-linked immunosorbent assay was used to determine the incidence of HIV-1 subtype C infection among women attending public sector antenatal clinics in Hlabisa, a rural district in KwaZulu-Natal, South Africa. The STAHRS results were confirmed by using a mathematic model to obtain an independent estimate of the age-specific incidence rates from the age-specific prevalence data. The data reveal extraordinarily high HIV-1 incidence rates in South Africa. In 1999, the annual incidence of HIV-1 among susceptible women aged 15 to 49 years standardized to the age distribution of adult women in Hlabisa was 17%. Incidence peaked among 22-year-old women at 24% per year. The HIV-1 incidence rates provide valuable additional information indicating that new infections are continuing unabated and that the HIV-1 epidemic is still growing in rural South Africa.