The objective of the study was to determine the association between BCG immunization and severe tuberculosis (TB). We performed a retrospective study, including medical records from patients of the pneumology department at the National Children's Institute in Peru, between the years 1990-2000. A total of 2106 TB cases were reviewed, from them 259 patients were severe (miliary TB or meningoencephalitic TB). From all, 497 cases did not have history of BCG vaccination, 202 had severe TB and 295 non-severe TB (OR = 0.05, 95% CI = 0.03 to 0.07). In conclusion, children diagnosed with TB and who have been immunized with BCG, has 94% lower risk of developing severe TB, compared to children with TB non-immunized with BCG.