We report a case with Langerhans cell histiocytosis appearing as an extra-pleural tumor. A 20-year-old man was transferred to our hospital because of right chest pain and fever. His chest X-ray showed an extra-pleural mass and chest CT scan showed a mass lesion with right 7th rib fracture. 67Gallium and bone scintigram showed uptake at the same site. We performed a CT-guided puncture biopsy. Pathological findings of the specimen showed diffuse proliferation of histiocytoid cells with some eosinophils. The histiocytes were positive for S-100 protein and CD1a on immunohistochemical stain. Langerhans cell histiocytosis was diagnosed. There was no other involvement of the disease except the rib. The tumor resolved only with smoking cessation and no recurrence was observed during the follow-up period. An association between smoking and progressions of the rib disease was suggested.