Four cases of paraganglioma in the thorax, consisted of 3 cases originating from the mediastinum and a case of pulmonary metastasis from the posterior peritoneum, were clinically investigated. Three were malignant and one was benign with noradrenaline secretion. On surgical excision, preoperative arterial embolization was assumed to be useful for reducing hemorrhage during procedure. Pre and intra-operative circulatory management was also mandatory in case of functioning paraganglioma. Of the 3 malignant cases, 2 survived for more than 10 years with radiotherapy alone or surgical resection of multiple metastatic nodules in the bilateral lungs. The other one, though inoperable due to extensive invasion to right and left atria, showed highly sensitivity to intra-arterial infusion chemotherapy of CDDP. These results suggested that long term survival might be expected even in metastatic or inoperable cases. There were no reliable histologic features distinguishing malignant from benign tumors, however 2 malignant cases with local invasion showed aneuploid patterns in the DNA histograms, which might offer a adjunct possibility in the assessment of malignancy.