We report a case of resected plasma cell (PC) type Castleman's disease (CD) in a 21-year-old female who had an anterior mediastinal mass with additional surrounding nodules. She was aware of low-grade fever and fatigue for several years. From hematological and biochemical examinations, elevated inflammatory responses and levels of serum IgG (2908 mg/dL) and IL-6 (22.2 pg/mL) were observed. She was diagnosed with PC type CD by needle biopsy under computed tomography (CT) guidance. It was thought that the lesion was localized in the mediastinum. Then, mediastinal adipose tissue including the tumor, additional nodules and thymus were removed. The histological findings of PC type CD were found not only in the main tumor but also in surrounding swollen lymph nodes. Her symptoms improved and inflammatory responses decreased after the operation. No recurrence has been observed for 5 years after the operation.