BACKGROUND: HIV infection increases the risk of tuberculosis. The HIV epidemic is also likely to have an indirect effect on the incidence of tuberculosis because of the increased number of infectious individuals in the population. This should be apparent as an increase in tuberculosis among HIV-negative individuals, but this has not previously been demonstrated directly. METHODS: A retrospective cohort study was conducted in four gold mines in South Africa, including all miners who had HIV tests in 1991-1997. Tuberculosis was detected by annual screening, contact tracing and self-presentation of symptomatic patients. RESULTS: The annual incidence of new pulmonary tuberculosis in the mines rose from 0.53% in 1991 to 1.0% in 1997. The HIV status was known for 23 874 miners, of whom 3371 were HIV positive on entry and 2737 seroconverted during follow-up. The incidence of tuberculosis was higher among HIV-positive miners than HIV-negative miners from 1992 onwards, and the proportion of tuberculosis attributable to HIV increased from 0% in 1991 to over 40%. The incidence of tuberculosis increased in HIV-negative miners from 1995 onwards; incidence in the late 1990s was double that in the early 1990s. CONCLUSION: HIV infection has dramatically increased the incidence of tuberculosis. There was a direct increase in those who were HIV infected, but also a doubling in tuberculosis incidence in those remaining HIV negative, implying considerable ongoing Mycobacterium tuberculosis transmission. This has occurred despite active case finding and directly observed therapy, which exceeds WHO targets for cure rates. Further interventions targeted at both HIV and tuberculosis are needed.