Neonatal BCG vaccination has long been offered routinely to children born at St Mary's Hospital (SMH), Manchester, England, whereas the city's other obstetric hospitals have generally restricted this procedure to children of Asian origin and those with a family history of tuberculosis. Among children aged 0-14 years who had been born to Manchester residents in 1965-80, 65 presented with tuberculosis in 1975-80 whilst still resident in the city. The estimated incidence rate was less than half as high among all children born at SMH as among those not born there, largely because the rate for those born and vaccinated at SMH was less than one-quarter of that for those born elsewhere. Children with Bangladeshi, Indian, or Pakistani surnames also shared in the reduced risk associated with vaccination. These findings strongly support the effectiveness of neonatal BCG vaccination.