Castleman's disease is a rare, benign disorder most commonly located in the mediastinum as a solitary mass. It is a lymphoid tissue disorder characterized by lymphoid proliferation. In this paper we describe a case of asymptomatic interlobar fissure tumor, localized Castleman's disease, hyaline vascular type, in a 30-year-old female. The tumor arose from the interlobar fissure between the right middle and lower lobes. Laboratory data revealed hypochromic microcytic anemia, similar to that found in iron deficiency, and an elevated erythrocyte sedimentation rate. She underwent video-assisted thoracic surgery for excision of the tumor. Anemia disappeared two months after surgery. No recurrence of the lung tumor was seen 19 months following surgery and she remains well.