Although the directions in surgical writings are clearly laid down concerning the course to be pursued when pregnancy and labour are complicated by an ovarian tumour, the difficulty which often confronts the operator when he is face to face with the actual case is uncertainty regarding the nature of the tumour. Although he may begin the operation under the impression that he has to deal with an ovarian tumour, it may turn out to be a fibroid, a tumour of the pelvic wall, a misplaced spleen or kidney, a tubal pregnancy, a sequestered extra-uterine fœtus (lithopædion), or a calcified hydatid cyst. Thus an expected ovariotomy may terminate as a Cæsarean section, or as a hysterectomy. In many cases the surgeon must rely on his own judgment and experience, but it may be useful to furnish some directions which may help him. It may be useful also to mention what unexpected conditions are sometimes found. Thus an experienced gynæcologist like Prof. Olshausen once removed a gravid uterus under the impression that it contained a cystic fibroid which would obstruct delivery. When it was examined after removal, the suspected fibroid proved to be a large sacral teratoma growing from the fœtus. =Ovarian tumours and pregnancy.= Before the fourth month of pregnancy, single and double ovariotomy is attended with a low rate of mortality, and the risk of disturbing the pregnancy is small. The removal of a parovarian cyst during pregnancy is more liable to be followed by abortion than single or double ovariotomy. After the fourth month the risk is that of an ordinary ovariotomy, but the chances of abortion increase with each month. It is also a fact that ovariotomy may be safely carried out between the eighth and ninth months of gestation without precipitating labour, even when the tumour is incarcerated in the pelvis. In many cases in which ovariotomy is urgently indicated during pregnancy, the pedicle will be found twisted. When the tumour is situated above the uterus there is rarely any difficulty in dealing with it, as the pedicle is usually long, but it will require extra care in applying the ligature, as the tissues, being unusually vascular and soft, are easily lacerated. Occasionally the tumour lies in the pelvis below the uterus: in this case the surgeon carefully insinuates his hand between the pelvic wall and the uterus, and then gently withdraws the tumour from its incarcerated position. CASES IN WHICH OVARIOTOMY HAS BEEN PERFORMED NEAR THE END OF THE NINTH MONTH OF PREGNANCY