(1) Malignant disease of the Mediastinum is not such a rare disease as is generally supposed but innocent tumours of the mediastinum are exceedingly rare in this country. (2) It is essentially a disease of early middle age but it may occur at any age. (3) It seems to be slightly increasing in frequency. (4) The disease is twice as common in males as in females. (5) A definite tuberculous history is very commonly found. ( 6) A malignant family history is often present but not so commonly as a tuberculous. (7) Though tubercle bacilli are usually not found in the sputum still there is probably some obscure relationship between pulmonary tuberculosis and new growth of the mediastinum. (8) The anterior mediastinum is the common seat of origin. (9) Sarcoma is the commonest form of malignant disease of the mediastinum in both sexes and it usually takes the form of Lynphosarcoma. (10) Carelnoma of the Lnediastinum is relatively speaking much commoner in females than in males. (11) The lungs are practically always affected sooner or later and pulmonary symptoms are usually present. (12) The right lung is much more commonly affected than the left. (13) Extra thoracic Metastases are very common and often very palpable. In any case suggesting: mediastinal new growth palpation of the abdomen is of the greatest diagnostic significance. (14) A middle aged person with obscure pulmonary symptoms or with symptoms out of proportion to the physical signs should be submitted to a careful and thorough examination and not hastily diagnosed as neurosis. (15) A diagnosis is quite within the limits of the ordinary practitioner and no scientific or difficult tests are necessary in making a diagnosis strongly pointing to the condition. (16) If pyrrhexia is present it is due to some complication supervening upon, or caused by, the original condition. (17) Microscopic examination of the sputum is rarely of great diagnostic value but the persistent absence of tubercle bacilli in the sputum of a case suggesting pulmonary tuberculosis is very significant. (18) Haemoptyses is a moderately common symptom. (19) Careful percussion is of the greatest importance. (20) A pleural effusion is very often present and it is often haemorrhagic but a haemorrhagic effusion is not as pathognomonic of the condition as older observers believed. (21) Microscopic examination of the pleural fluid should always be done but it is rarely of diagnostic importance. (22) A large proportion of small lymphocytes in a pleural effusion is quite as characteristic of malignant disease as of pulmonary tuberculosis. (23) Laryngoscopic examination is of the greatest importance in detecting early signs of pressure and may be of great value even before any vocal defect can be detected by the ear. (24) X-rays and the bronchoscope are of great value in the hands of an expert in making an early diagnosis. (25) The disease is usually fatal in less than a year and exhaustion is the common cause of death. (26) At the present time treatment is practically entirely palliative. In all probability radium has a great future before it and provided on early diagnosis be made radical surgical measures may at any rate prolong the life of the patient.