We present a rare case of a 16-year-old male patient with Castleman's disease (CD) manifest by a suspicious mass within the left suprarenal region abutting the left adrenal gland, mimicking an adrenal neoplasm. CD is an uncommon and poorly understood lymphoproliferative disorder that, when observed, typically occurs as a mediastinal mass. Two percent of cases reportedly occur in the pararenal region. Although rare, Castleman's disease should be considered in the differential diagnosis of a retroperitoneal mass.