The tumors of the mediastinum which are supposed to be most common are readily recognized by the roentgen ray. They include the various neoplasms involving the mediastinal glands, substernal thyroid adenomas, aneurysms, dermoids and other tumors. In the case of the lipoma, however, a shadow is not revealed unless it is large. It has occurred to us, therefore, that fatty tumors may actually be much more frequent than the few references to them in the literature would indicate, especially since it might be easy to overlook them at postmortem examination unless they were unusually large. Their clinical importance lies in their ability to produce effects of pressure, and they should be considered as possible causes of symptoms in those cases in which there is perhaps an otherwise unexplained choking sensation, a recurrent laryngeal paralysis or similar condition. Our attention was attracted to these possibilities by a recent case. REPORT OF