Thirty-one paragangliomas of the cauda equina region were studied (18 men and 13 women, ages 30-71 years [mean, 51 years]). Symptoms (1 day to 15 years in duration; mean, 48 months) included low back pain (87%), sensory/motor deficits (35%), urinary/fecal incontinence (13%), and paraplegia (6%). All patients studied had some myelographic block. Cerebrospinal fluid protein level ranged from 56 to 7000 mg/dl (mean, 1109 mg/dl). Most tumors were limited to the filum terminale, although one also involved the conus medullaris and two clearly arose from a caudal nerve root. All but one were entirely intradural. The tumor was totally excised in 26 cases; these patients remain disease-free. Of three patients whose tumors were excised subtotally, two received radiotherapy; the one non-radiated patient died of tumor-related complications. No autopsy was performed. One partially encapsulated tumor that had been subjected to biopsy and irradiation presented 1 year later with osseous invasion and retroperitoneal extension; 20 years after subtotal excision, this patient is alive but paraplegic. Morphologically, all tumors resembled paraganglioma at other sites. Cytologic atypia and mitotic activity generally were absent to mild. Fourteen (45%) cases showed ganglionic differentiation. All tumors tested were immunoreactive for neuron-specific enolase and neurofilament protein, and most showed somatostatin or serotonin reactivity. S-100 protein immunoreactivity was noted in sustentacular cells and, to a lesser extent, within chief cells and neurons. The authors conclude that paragangliomas are largely benign and encapsulated and respond to simple resection. When surgically feasible, gross total removal should be the goal of surgery. When subtotal resection is necessary or when local invasion leaves a question as to completeness of tumor removal, irradiation seems mandatory although far from guaranteeing prevention of recurrence. Biopsy alone is undesirable.