The diagnosis of a malignant ovarian tumour can be made laparoscopically. It is particularly indicated in cases of ascites occurring by itself due to a neoplasm or of undiagnosed origin, and in cases of infiltration of the pelvic nodes or when a small abdominal mass, whether it is isolated or associated with ascites, is found. This particularly of value when a cytological examination of the ascitic fluid does not indicate the diagnosis. Laparoscopy is a means by which the degree of spread of abdomino-pelvic lesions can be discerned in cases where the malignant nature of the ovary is known, but where the prognoses for its removal, either immediately or after several cures with chemotherapy, are doubtful and where the degree of spread has not been correctly and precisely determined at the first surgical intervention. Therefore laparoscopy can complete the information obtained from pelvic examinations and avoid the need for carrying out an exploratory laparotomy, but is gives less information than this latter does about the degree of spread in the pelvis and in the abdomen. So, laparoscopy is a means by which repeated control of the results of therapy which is more thorough than clinical examination can be assured, particularly because it acts as a check on peritoneal cytology. Although its interpretation can be very difficult and its reliability is a relative one, the latter is a good criterion of follow-up.