This 32-year-old woman presented with pregnancy-related arterial hypertension unresponsive to antihypertensive therapy. During cesarean delivery, a lobulated retroperitoneal mass was discovered. 18F-FDG PET/CT performed 18 days postpartum demonstrated the hyperactive retroperitoneal mass and extensive hyperactivated brown adipose tissue. The mass was surgically removed, revealing a para-aortic multicentric paraganglioma. After surgery, blood pressure normalized, and serum chromogranin A and urinary metanephrines normalized. Brown adipose tissue hypermetabolism disappeared on follow-up FDG PET. Her initial FDG PET demonstrated brown adipose tissue hyperactivation, which may have been caused by the combination of hormonal changes in pregnancy and the paraganglioma.