There has appeared a considerable amount of literature attesting to the increasing frequency of primary intrathoracic neoplasm arising from the respiratory tract—lung and bronchi. This has emanated from various centres, both in Europe and in America. It had been thought that a similar increase was noticeable in Edinburgh, and some years ago Dr J. Davidson, then pathologist in the Royal Infirmary, did some work on the incidence of the disease as shown by the records of the institution. This was not recorded at the time, and it seemed desirable to extend that work and to publish yearly and quinquennial tables on the lines of Bonser's work, with very brief deductions, in order to ascertain so far as possible the actual state of affairs here and to give figures for comparison with those of other places. It is necessary to define the meaning of the term “intrathoracic tumours”. It has been chosen instead of “primary lung tumours” because in the earlier cases the “oat-celled” carcinomata were regarded as primary mediastinal gland sarcomata and have, therefore, had to be included, a point which recent microscopical examination of some of these earlier cases has shown to be justified. The records from 1904 to 1934 inclusive have been carefully searched, and only those cases have been included which were described as malignant and as arising from lung or mediastinal glands; cases of Hodgkin's disease, cancer of the oesophagus and thymic tumours were excluded.