Immune reconstitution inflammatory syndrome (IRIS) occurred in 16 of 37 antiretroviral-naive patients who were treated subsequently for tuberculosis and human immunodeficiency virus (HIV) type 1 infection. IRIS was related to increases in the CD4 cell percentage and in the ratio of CD4 cells to CD8 cells after 1 month of antiretroviral therapy and to dissemination of tuberculosis. These results have implications for the diagnosis of IRIS and the understanding of its pathogenesis.