Mass BCG Vaccination is an effective and an inexpensive method of tuberculosis control. In Singapore, a nation wide BCG Vaccination programme was implemented in 1957, and from 1957 to 1972, i.e. a 16 year period, over 1 million vaccinations had been performed: 680,098 for infants, 512,797 for school students, 49,417 for contacts of tuberculosis patients and 7,775 for other special groups. The coverage of newborn infants has been over 90% from 1967 to 1972. In 1972, it was estimated that 90% of primary school children and 75% of secondary school students have been covered with BCG vaccinations. Although no controlled studies have been done in Singapore, it is observed from our analysis that the BCG programme has contributed in no small measure to the decline in tuberculosis incidence and mortality rates. Thus for 1972, the tuberculosis incidence rates per 100,000 were 5 for the BCG vaccinated group and 37 for the non-vaccinated group of primary school students, and 34 and 127 for the corresponding groups of secondary school students. In 1956, the death rate per 100,000 of respiratory tuberculosis was 4 and that of non-respiratory tuberculosis was 23 for children aged 4 and below, and the corresponding rates were 0.5 and 6.7 for those aged 5 to 9, and 0.8 and 3.7 for the group aged 10 to 14. In 1971 there were no tuberculosis deaths in children under 10 years of age, and the death rates for the age group 10-14 were 0.3 per 100,000 for either form of 241 tuberculosis.