Eosinophilic granuloma limited to the lung has not to our knowledge been previously reported. Two histologically proved cases recently observed, and carefully followed, are recorded in the following pages. Eosinophilic granuloma involving both lung and bone, diagnosed by biopsy of the osseous lesions, has been reported on three occasions (6, 8, 9). To these three cases another is added. The cases presented here have all been confirmed by surgical biopsy and histologic study. This, we believe, is the first report of histologic confirmation of the lung lesion. Finzi (1), in 1929, recorded the first case of eosinophilic granuloma of the bone. His diagnosis was“a myeloma with preponderance of eosinophilic cells.” Otani and Ehrlich (5) and Lichtenstein and Jaffe (3) established the condition as an entity in 1940. Since these early descriptions there has been a tendency to expand the entity to include cases in which there are multiple bone lesions and even extra-osseous lesions, such as those involving lymph no...