Sinus histiocytosis with massive lymphadenopathy or Rosai-Dorfman disease(RDD) is a rare type of histiocytosis syndrome, that presents in its most typical form as massive, painless, bilateral lymph node enlargement in the neck during the first or second decade of life. The disease involves extranodal site in over 25% to 43% of the cases, however cases of extranodal RDD without nodal disease have rarely been reported. The involved sites of extranodal RDD have been reported various that were orbit, ocular adnexae, head and neck, upper respiratory tract, breast, gastrointestinal tract, CNS, etc. A 35 year-old man was present with pleural pain on left anterior chest and anterior mediastinal mass, that underwent an excision to remove the suspected invasive thymoma, and the diagnosis was confirmed to extranodal Rosai-Dorfman disease.