Castleman's disease (CD) is an atypical lymphoproliferative disorder characterized by hyperplasia of lymphoid tissue that may develop at a single site or throughout the body. This disorder has frequently been associated with several systemic syndromes, including human immunodeficiency virus infection, polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy and skin changes (POEMS) syndrome and various connective tissue diseases. However, there have been no previously reported cases of concomitant sarcoidosis and CD. In this report, the authors describe a young woman with an enlarging neck mass, biopsy of which showed histopathological features consistent with the hyaline vascular type of CD along with the presence of non-necrotizing granulomas and was deemed unresectable due to encasement of vital neural and vascular structures. Further studies revealed hypermetabolic generalized lymphadenopathy with pulmonary perilymphatic nodules. Bronchoscopic investigations demonstrated the presence of non-necrotizing granulomas within the lung parenchyma and mediastinal lymph nodes, a CD4(+) T-lymphocyte predominant bronchoalveolar lavage and an elevated CD4/CD8 ratio consistent with a concomitant diagnosis of sarcoidosis. Institution of immunosuppression with prednisone and methotrexate led to reduction in size of the neck mass that allowed radical curative resection of the CD.