Summaryo(1)150 consecutive cases of pulmonary tuberculosis and pregnancy, confined in the Grove Park/Lewisham Hospital Unit (London), are studied.(2)127 cases were of active disease and most of these were of moderately or advanced chronic disease.(3)71 per cent of the active cases worsened during the pregnancy. Of 30 cases of haemoptysis in this pregnancy, there were 12 in the first trimester, 13 in the second, and 5 in the last three months.(4)By full term it was estimated that 63·8 per cent of active cases were improving and 13·4 per cent were deteriorating.(5)Deterioration in the first two months following delivery occurred in 43 per cent of active cases. None of the 23 quiescent cases are known to have deteriorated. Of those 49 cases which relapsed, 21 had been regarded as improving at term, 16 had been worsening but deteriorated more rapidly afterwards. 53·5 per cent of the ‘B2’ cases and 78·6 per cent of the ‘B3’ cases deteriorated in this period.(6)Deterioration in the puerperium was classified as follows: —(i) Death; (ii) x-ray changes, viz. (a) spread of disease, (b) flare-up of foci, (c) ‘breaking down’ of a solid focus, (d) enlargement of a tension cavity, (e) acute pleural effusion; (iii) Sputum becoming positive without x-ray changes; (iv) Constitutional deterioration without the above changes.(7)In nearly half the cases with ‘tension’ cavities, the cavity enlarged after delivery.(8)Cases of advanced disease, those with tension cavities, and those with ‘so-called’ ‘blocked’ cavities or solid foci are more liable to break down post-partum.(9)The descent of the diaphragm may have some influence on the reactivation of tuberculous foci.(10)Pulmonary tuberculosis in pregnancy should be treated according to accepted principles, but the disease should be regarded more seriously and deterioration in the puerperium may well occur. 150 consecutive cases of pulmonary tuberculosis and pregnancy, confined in the Grove Park/Lewisham Hospital Unit (London), are studied. 127 cases were of active disease and most of these were of moderately or advanced chronic disease. 71 per cent of the active cases worsened during the pregnancy. Of 30 cases of haemoptysis in this pregnancy, there were 12 in the first trimester, 13 in the second, and 5 in the last three months. By full term it was estimated that 63·8 per cent of active cases were improving and 13·4 per cent were deteriorating. Deterioration in the first two months following delivery occurred in 43 per cent of active cases. None of the 23 quiescent cases are known to have deteriorated. Of those 49 cases which relapsed, 21 had been regarded as improving at term, 16 had been worsening but deteriorated more rapidly afterwards. 53·5 per cent of the ‘B2’ cases and 78·6 per cent of the ‘B3’ cases deteriorated in this period. Deterioration in the puerperium was classified as follows: — (i) Death; (ii) x-ray changes, viz. (a) spread of disease, (b) flare-up of foci, (c) ‘breaking down’ of a solid focus, (d) enlargement of a tension cavity, (e) acute pleural effusion; (iii) Sputum becoming positive without x-ray changes; (iv) Constitutional deterioration without the above changes. In nearly half the cases with ‘tension’ cavities, the cavity enlarged after delivery. Cases of advanced disease, those with tension cavities, and those with ‘so-called’ ‘blocked’ cavities or solid foci are more liable to break down post-partum. The descent of the diaphragm may have some influence on the reactivation of tuberculous foci. Pulmonary tuberculosis in pregnancy should be treated according to accepted principles, but the disease should be regarded more seriously and deterioration in the puerperium may well occur.