Mutations of SDHD lead to head and neck paragangliomas (HN-PGL), mainly benign tumors of the carotid body and other parasympathetically innervated paraganglia, but may also lead to tumors of the adrenal medulla (pheochromocytoma) and the sympathetically innervated paraganglia (extra-adrenal paraganglioma), some developing into aggressive metastatic cancers. The gene discussed is SDHD; the disease is hereditary pheochromocytoma-paraganglioma.