In order to better elucidate the lesser known aspects of the biological behavior and prognosis of supratentorial ependymomas in children and young adults, we studied a series of 20 patients, ages 1 to 20 years. The tumor site was extraventricular in 14 cases and intraventricular in 6 (including one third ventricle tumor). Histologically, according to World Health Organization criteria, there were 12 ependymomas (E), 2 subependymomas (SE), and 6 malignant ependymomas (ME). Of the 18 patients surviving surgery, 12 (66.6%) are alive and disease free 63 to 252 months (mean, 146 mo) after the operation; 9 harbored an E, 2 had an SE and 1 had an ME. Four patients are now out of risk of recurrence according to Collin's law. Six of the long-term survivors (50%), four E and two SE, did not receive postoperative radiotherapy. However, two patients with E, initially treated by surgery alone, had a recurrence and one subsequently died. Two ME patients showed signs of spinal metastases after subsequent operation for recurrence and shortly before death. Considering the partially good results as well as failures after surgery alone in our and in other series and the risks of irradiating the child's brain, we tried to elucidate in what cases radiotherapy could be reasonably withheld, or alternatively, when prophylactic craniospinal irradiation should be prescribed. The main conclusions of our study are the following: 1) Radical surgery alone is a reasonable option as the initial treatment for lateral ventricle tumors and for solid extraventricular tumors located far from eloquent brain areas, provided the histology is benign, especially if of the SE type.(ABSTRACT TRUNCATED AT 250 WORDS)