Tuberculosis characteristics and incidence were assessed among patients with concurrent human immunodeficiency virus infection and chronic hepatitis C virus infection who were receiving interferon-based therapy at 3 hospitals in Spain. Four of 570 patients (0.7 cases per 100 person-years; 95% confidence interval, 0.19-1.78 cases per 100 person-years) received a diagnosis of tuberculosis; all of them presented with a decrease in CD4+ cell count before diagnosis, and 3 of them received a delayed diagnosis. After tuberculosis treatment, all patients were cured.