BACKGROUND The aim of this study was to determine the risk of active tuberculosis in intravenous drug addict (IVDA) patients seropositive and seronegative for the HIV. METHODS A retrospective study of a cohort of IVDA males in 2 drug addict detoxication communities was carried out. Patients with tuberculosis, under treatment or chemoprophylaxis for tuberculosis and those with a stay of less than 3 months were excluded. Patients included underwent a serologic study to detect antibodies versus HIV and a Mantoux test with 2 U. PPDRT23. Subjects who were HIV+ with a Mantoux test < 5 mm were given a delayed cutaneous sensitivity test with 7 antigens. The incidence index of tuberculosis was studied. Logistic regression analysis was performed to evaluate the relative risk of tuberculosis in HIV+ controlled by other variables (having been in prison, previous liver disease, country of origin, age, length of IVDA and length of follow up). RESULTS Of the 198 patients admitted 132 were included. Forty-seven were HIV+ and 85 HIV-. Fourteen of the former (30%) and 44 of the latter (51%) had a positive reaction to the Mantoux test (OR 0.4; confidence interval 95% 0.18-0.92; p < 0.05). Eight seropositive (17%) patients with a negative Mantoux test presented anergia to the delayed cutaneous sensitivity tests. After a mean follow up of 12.0 +/- 9.0 months, 4 patients out of the 47 HIV+ (8.5% or 6.93 cases/100 individuals/year; CI 95% 0.13-13.72) presented tuberculosis versus none of the 85 HIV- (p < 0.05) patients. Of the 4 patients diagnosed of tuberculosis, the initial reaction to the Mantoux test was negative in 2 (one pulmonary and the other milliar tuberculosis). Two of the 4 patients diagnosed of tuberculosis died. CONCLUSIONS The risk of active tuberculosis is specially high in HIV seropositive intravenous drug addicts. The response to the Mantoux test has little sensitivity for demonstration of tuberculous infection in HIV seropositive patients.