The risk of developing tuberculosis is dependent on both the risk of being infected and the risk of infection leading on to active disease. The former will depend on the incidence of tuberculosis in the community where the individual lives or works. The latter will depend on many factors impinging on the individual both genetic and environmental. The greatest single risk factor for developing tuberculosis from infection is concurrent HIV infection. Where these two infections are prevalent tuberculosis case rates have risen dramatically and will continue to do so unless either infection can be curtailed.