In order to assess the effect of war conditions upon the incidence of tuberculosis in London, the authors undertook a review of the notification records. As compared with 1938, there was in 1941 an increase of 43% in the rate of occurrence of new cases of pulmonary tuberculosis and of 15% in new cases of nonpulmonary tuberculosis. The pulmonary tuberculosis death rate increased over the same period by 72% and the nonpulmonary rate by 67%. These increases are much greater than for England and Wales as a whole. Children were affected much more than adults, particularly in the non-pulmonary type. At ages over 25, [male][male] have been more affected than [female][female]. No appreciable difference in the sexes could be established in the below 25 age group. The increase in nonpulmonary tuberculosis has occurred almost equally in all the principal sites, except in abdominal tuberculosis, in which the increase was significantly lower. Considering the finding that new cases of pulmonary tuberculosis increased more in adults than new cases of nonpulmonary disease, whereas the increase in children was marked in the nonpulmonary sites, lead the authors to conclude that contact and droplet infection has been an important feature in London. The factors influencing the incidence of tuberculosis include changes in the age and sex distr. of the population as a result of evacuation and of recruitment to the Forces, the strain and overcrowding resulting from bombing, fatigue and lack of rest, restriction of diet, and, on the other hand, increased employment and financial resources for those formerly on the verge of poverty. In mental hospitals the increased incidence is greater than in the population as a whole.