Paragangliomas of the retroperitoneum arise from specialized neural crest cells distributed along the aorta in association with the sympathetic chain. In order to ascertain characteristic CT features of extraadrenal retroperitoneal paragangliomas to differentiate them from other retroperitoneal tumors, 31 discrete tumors and two cases of paragangliomatosis in 28 patients were reviewed retrospectively, and the CT features were correlated with clinical and pathologic findings. There were 16 men and 12 women. Average age was 37 years (range, 11-70 years). Twenty-four patients (86%) had hypertension. Of these, catecholamine levels were elevated in all 18 patients who had biochemical studies. Four patients (14%) had malignant paragangliomas. The discrete tumors were classified by location as suprarenal (26%), renal hilar (32%), or infrarenal (42%). Suprarenal paragangliomas could not be distinguished from the ipsilateral adrenal gland on CT. The average size of functional tumors was smaller (7.0 cm) than that of nonfunctional tumors (12.0 cm), but the sizes of the two groups overlapped. Smaller tumors were more likely to be homogeneous and have well-defined margins than were larger tumors. Our findings indicate that extraadrenal retroperitoneal paragangliomas are functionally active more often than previously reported and that they are readily detected by CT as soft-tissue masses closely associated with the entire length of the abdominal aorta. However, no CT feature was found that was unique for paraganglioma.