Castleman's disease is a rare disorder characterized by benign proliferation of lymphoid tissue. Most cases occur as a mediastinal mass, although extrathoracic involvement including nodal and extranodal locations has been reported. The left suprarenal location of this localized disease may be mistaken for an adrenal tumor. We report a case of a 51-year-old woman with a Castleman's tumor located superomedial to the upper pole of the left kidney that mimicked an adrenal neoplasm.