Extraadrenal retroperitoneal paragangliomas: natural history and response to treatment. Extraadrenal retroperitoneal paragangliomas (RP) are uncommon tumors. Because of their rarity, little is known of their natural history or response to treatment. We reviewed 22 patients with RP who were seen at our center between 1949 and 1990. The distribution of male and female patients was nearly equal, and the mean age was 42. Most patients were admitted with pain or a mass, and eight of 22 tumors were functional. No significant difference was noted in duration of symptoms, size of the tumor, or survival between functional and nonfunctional tumors. Eleven of 22 (50%) RP metastasized and were therefore classified as malignant. Five-year and 10-year disease free survival rates were 19% and 19% for tumors not resected and 75% and 45% for those completely resected. Once metastases occurred, the 5-year survival rate was 36%, but no patient survived beyond 76 months. Predictors of survival included complete resection of the tumor but not size or functional status. Although some patients who received chemotherapy or radiotherapy had clinical responses, a survival benefit could not be shown. RP have a high rate of malignant behavior and should be treated aggressively with operation. Late metastases are not uncommon, and prolonged follow-up is necessary. Once metastases have occurred, some patients may have prolonged survival. 