Paradoxical reactions during tuberculosis are defined by exacerbation of clinical symptoms or laboratory or radiologic abnormalities during antituberculosis treatment or when an antiretroviral treatment is added to it. This phenomenon does not involve relapse of the opportunistic infection but rather a reconstitution of an abnormal immune response. The phenomenon is relatively frequent after antiretroviral treatment begins in HIV-infected patients with tuberculosis. Diagnosis, based on a group of heterogeneous clinical and/or radiologic criteria, is often difficult. Although outcome is most often spontaneously favorable, complications are possible. Treatment relies on the maintenance of specific treatment of the pathogen responsible for the opportunistic infection, the antiretroviral treatment, and possibly the addition of corticosteroid therapy.