A hospital-based case-control study was carried out at the Vilela Children's Hospital in Rosario, Argentina, to measure the protection conferred by BCG vaccination against tuberculosis (TB). The study included 148 newly diagnosed cases of TB (75 males and 73 females, mean age 3.34+/-2.97 years, S.D.), 134 of them with pulmonary TB and 14 cases with extra-pulmonary disease. Controls (425 males and 357 females, 3.39+/-2.98 years) were selected randomly among children who attended to the Hospital showing, neither respiratory diseases nor any other infectious illnesses. Information on BCG vaccination history was assessed from scars or immunisation records. All participants were negative to human immunodeficiency virus and belonged to the lower and upper-lower socioeconomic status, being similar in place of residence and ethnic characteristics. Rate of vaccinated children was 92.6% of cases and 94.5% of controls (3.4 and 3.9% of them without scars, respectively). Regarding the total cases, the protective association between BCG and TB was statistically insignificant, as was for the pulmonary form. Among cases with extra-pulmonary disease, vaccine effectiveness attained significance [79% (95% CI=26-94)], no matter their age, sex or nutritional status. BCG vaccination exerted a beneficial role in extra-pulmonary TB, even in children not seriously undernourished.