Surgery retains an important place in the treatment of malignant germ cell tumours of the mediastinum though in order to achieve complete excision the appropriate moment for surgery needs to be chosen carefully. Complete excision, which is the great benefit of surgery, is rarely possible as first treatment because of the large volume of these tumours and their extension into mediastinal vascular structures. Considerable surgical experience is essential in order to allow extended incision involving the lung and the large vessels which might involve prosthetic replacements. Excepting in situations of greast urgency surgery usually follows chemotherapy and is used as follows: - in patients who appear to be in complete remission but who have residual lesions which require eradication, and those with malignant tissue which is persisting or more often of a mature teratoma which may have a risk of Progressing. The return of tumour markers to normal values does not guarantee the absence of some residual cancer, - in some patients with a partial remission complementary surgery may allow a further 20% to achieve a complete response', - in the absence of a response to chemotherapy, surgical excision should be attempted without too long a delay and then followed by a different chemotherapy regime.