Follicular dendritic cell sarcoma is a rare and aggressive tumor and its management is a major clinical challenge. Surgery is considered the mainstay of treatment and no adjuvant approach has demonstrated the ability to reduce the rate of relapses. We report on a case of a man with a 26-year clinical history of mediastinal follicular dendritic cell sarcoma, with several relapses after multiple surgical interventions. The impact of chemotherapy was very small, unlike the radiation therapy that was performed twice, with an interval time of 8 years, through an intensity-modulated technique and an altered fractionation schedule.