Castleman's disease (CD), also known as giant lymph node hyperplasia or angiofollicular lymph node dysplasia, is a rare benign immunoproliferative disorder. CD is classified by histopathologic appearance (hyaline vascular, plasma cell or mix variant) as well as by the number of lymph nodes that are involved (unicentric and multicentric). We report the case of a 24-year-old female who was found to have unicentric anterior mediastinum CD. This article describes the clinical features, pathogenesis, diagnosis, and current treatment modalities for this uncommon disease.