Tuberculosis and HIV continue to be the world-leading killers among infectious diseases, primarily affecting poor people in many developing countries. Despite differences in the immunopathogenesis of human infection with tuberculosis and HIV, experimental evidence from clinical studies and relevant animal models can be used to reflect on the cellular mechanisms responsible for an increased risk of active tuberculosis among HIV-infected individuals. In this review, we will discuss the molecular features and regulation of cytolytic T cells and how deficient cytolytic T cell responses contribute to the pathogenesis of TB and HIV infection as well as TB/HIV co-infection. (C) 2010 Elsevier Inc. All rights reserved.