Erdheim-Chester disease (ECD) is a rare, non-Langerhans cell histiocytosis of unknown etiology, characterized by multiple organ involvement. Erdheim-Chester disease is usually diagnosed on the basis of characteristic radiologic and histopathological findings. Lesions may be skeletal or extraskeletal and may involve the skin, lung, heart, and central nervous system. In this article, we report a 62-year-old male case admitted with the complaints of cough and dyspnea. Imaging studies showed multiple osteosclerotic lesions of the bones, a large amount of pericardial effusion, and a mass which surrounds the right atrium. Cytological examination of the pericardial effusion material revealed foamy histiocytes with multinuclear giant cells. Pericardium and internal mammary artery biopsies showed fibrosis with infiltrating foamy histiocytes which were MAC38(+) and S100, CD1a(-) immunohistochemically. Based on these findings, the patient was diagnosed as ECD with extraskeletal manifestations and treated with systemic corticosteroids and chemotherapy (cyclophosphamide).