A right carotid body paraganglioma (CBP) was removed from a 30-year-old female after finding metastases to cervical lymph nodes. The tumor and its metastases were studied by light and electron microscopy to determine the neoplastic cell type. Light microscopy confirmed the presence of chief cells but was inadequate alone to exclude sustentacular cells. By electron microscopy, only chief cells were found in both the primary and secondary tumors. This is the first report of an ultrastructural study of a metastasis from a malignant CBP. From our observation, we suggest that CBP be defined as a proliferation of chief and sustentacular cells. Electron microscopy is essential to determine the cell types present and thereby help classify the lesion as a tumor or hyperplasia of the carotid body.