Objective: The differential diagnosis of retroperito-neal tumors includes lymphoid, germ cell, and neurogenic tumors such as paraganglioma. Paragangliomas are rare neuroendocrine tumors of the autonomic nervous system, which may secrete catecholamines and their metabolites. Clinical features include sustained or paroxysmal hypertension, headaches, sweating, and palpitations. Here we present an unusual case of a retroperitoneal tumor entrapping a sympathetic nerve ganglion and mimicking paraganglioma. Methods: A 57-year-old man with a history of controlled hypertension presented with paroxysms of tachycardia, flushing, high blood pressure, and headache. Ambulatory blood pressure monitoring showed uncontrolled labile hypertension with a normal nocturnal dip. Abdominal computed tomography (CT) demonstrated a 6.1 cm mass in the right retroperitoneum with adjacent lymphadenopathy. Paraganglioma was suspected and 24-hour urine demonstrated elevated normetanephrines (575 mcg/24 hours; normal, 5 to 290 mcg/24 hours) and vanillylmandelic acid (8.3 mg/24 hours; normal, 0.5 to 6.6 mg/24 hours). 68-Gallium DOTATATE positron emission tomography/CT showed weak uptake in the retroperitoneal mass and no other mass lesions. Results: Following preparation with alpha-adrenergic blockers, surgical excision was performed with diagnostic and curative intent. Postoperatively, hypertension and paroxysmal symptoms resolved completely. The histopathology report described seminoma with an entrapped large ganglion within the tumor. Conclusion: We describe a retroperitoneal seminoma with an entrapped ganglion causing hypertension and paroxysmal symptoms, with laboratory and imaging features compatible with paraganglioma. Awareness of the rare possibility of mechanical pressure on a ganglion, within the differential diagnosis of retroperitoneal mass and sympathetic symptoms may aid in clinical decision making in atypical cases.