In a patient with the clinical diagnosis of pheochromocytoma, the localization of the tumor is essential for planning treatment. Recently, we have performed I-123 metaiodobenzylguanidine (MIBG) adrenal scintigraphy in a patient presenting with a history of paroxysmal hypertension. Scintigraphy accurately located an ectopic unilateral pheochromocytoma. The scintigraphic diagnosis was confirmed by surgery and a diagnosis of ectopic unilateral pheochromocytoma was made by histopathological examination. This case report illustrates the specific diagnosis of pheochromocytoma by I-123 MIBG scintigraphy which is especially useful when other diagnostic procedures are equivocal.