The efficacy of the BCG vaccination campaign of neonates in Barcelona, carried out in the period 1966-1974, was evaluated with a study of cases and controls made during the period 1978-1988 in patients between the ages of 4 and 21 years. It shows that the efficacy of this vaccination campaign was 32%, that it was greater in men than women and that it decreased with the passage of time. The number of cases of tuberculosis prevented by this campaign is calculated at 13.4%. Given that the vaccine used offered maximum guarantees, the authors consider that this poor efficacy must be attributed to operational deficiencies in the vaccination campaign itself.