The number of patients co-infected with human immunodeficiency virus (HIV) and tuberculosis (TB) in our hospital is increasing year after year. Although most patients were HIV tested because of miliary tuberculosis or extra-pulmonary tuberculosis, some patients were found HIV seropositive by chance. In order to determine the incidence of HIV seropositivity among TB patients, HIV testing was carried out in TB patients for two years from January 1998 with the consent of patients. TB patients who received anti-HIV antibody examination were 164 in 1998, and 149 in 1999 and among them HIV seropositive TB patients were 4 in 1998 and 6 in 1999. The incidence of HIV seropositivity was 3.2% in all TB patients, 28.6% in miliary TB patients, and 1.0% in typical TB patients. The number of patients co-infected with HIV and TB in Tokyo was estimated by using these HIV seropositivity, it was 23 cases/year among miliary TB patients and 16 cases/year among typical TB patients. As there were many HIV-infected persons and many TB patients in Tokyo, it was thought that HIV testing in TB patients was important for the early detection of HIV infection and the early initiation of HIV treatment.